Electro-optical device having an electrophoretic medium containing an organic electroactive compound

Abstract

An electro-optical device having an electrophoretic medium containing an organic electroactive compound is provided. An electro-optical device comprising an electrophoretic medium containing charged pigment particles, a charge control agent, an organic electroactive compound, and a nonpolar liquid is disclosed. The electrophoretic medium is contained within a plurality of microcells. The composition of the electrophoretic medium allows for a reduction in the residual voltage of the electro-optical device and the degradation of the device's electrodes and other components, even after operations using DC unequilibrium waveforms.

Description

[Technical Field]

[0001] Related applications This application claims priority to U.S. Provisional Patent Application No. 63 / 535,471, filed on 30 August 2023, which, together with all other patents and patent applications disclosed herein, is incorporated in their entirety by reference. [Background technology]

[0002] Background of the Invention The present invention relates to an electro-optical device comprising an electrophoretic medium containing charged pigment particles, an organic electroactive compound, and a nonpolar liquid. The electrophoretic medium is contained in a plurality of microcells. The composition of the electrophoretic medium allows for a reduction in the residual voltage of the electro-optical device, even after operations using DC unequilibrium waveforms.

[0003] The terms “bistable” and “bistable” are used herein in their conventional sense in the art, and refer to a display including a display element having first and second display modes having at least one different optical property, wherein after any given element is driven with a finite-duration addressing pulse to assume either the first or second display mode, the state persists for at least several times, e.g., 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 grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and that the same is true for some other types of electro-optic displays. These types of displays are more appropriately called “multistable” than bistable, but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0004] The term “electro-optics,” when applied to materials or displays, is used herein in its conventional sense in the field of imaging technology, to refer to a material having first and second display states having at least one different optical property, wherein the material changes from the first to the second display state by the application of an electric field to the material. The optical property is typically a color perceptible to the human eye, but this may be a different optical property, e.g., a change in reflectance of electromagnetic wavelengths outside the visible range, in the case of a display intended for light transmission, reflectance, luminescence, or machine reading.

[0005] Some electro-optical media are solid in the sense that the material has a solid outer surface, but the medium may have, and often does have, an internal liquid-filled or gas-filled space. Displays using solid-state electro-optical media may hereafter be referred to as "solid-state electrophoretic displays" for convenience.

[0006] Several types of electro-optical displays are known. One type of electro-optical display is the rotating bichromal member type, as described, for example, in U.S. Patents 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 (this type of display is often referred to as a “rotating bichromal ball” display, but in some of the patents mentioned above, the rotating member is not spherical, so the term “rotating bichromal member” is more precisely preferred). Such displays use a number of small bodies (typically spherical or cylindrical) having two or more compartments with different optical properties and internal dipoles. These objects are suspended in liquid-filled vacuoles within a matrix, and since these vacuoles are filled with liquid, the objects can rotate freely. The appearance of the display is changed by applying an electric field, which rotates the objects into various positions and varies which parts of the objects are visible through the screen. This type of electro-optical medium is typically bistable.

[0007] Another type of electro-optical display uses an electrochromic medium in the form of a nanochromic film, which includes an electrochromic medium, for example, electrodes formed from at least partially semiconducting metal oxides, and a plurality of reversibly color-changing dye molecules attached to the electrodes. 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.

[0008] Another type of electro-optical 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 demonstrates that such electrowetting displays can be made bistable.

[0009] One type of electro-optical display that has been the subject of intensive research and development for many years is the particle-based electrophoretic display, in which multiple charged pigment particles move through a liquid under the influence of an electric field. Compared to liquid crystal displays, electrophoretic displays can have attributes such as good brightness and contrast, wide viewing angles, state bistability, and low power consumption. Nevertheless, their widespread use has been hindered by problems with the long-term image quality of these displays. For example, the particles that make up electrophoretic displays tend to settle, resulting in an insufficient lifespan for these displays.

[0010] As noted above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be produced using a gaseous fluid. 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. Such gaseous electrophoretic media appear to be susceptible to the same types of particle sedimentation problems as liquid-based electrophoretic media when the medium is used in a display where the medium is positioned in an orientation that allows such sedimentation, for example, when the medium is positioned in a vertical plane. In fact, particle sedimentation appears to be a more serious problem in gaseous electrophoretic media than in liquid-based ones, because the lower viscosity of gaseous suspensions compared to liquids allows for more rapid sedimentation of electrophoretic particles.

[0011] Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques used in encapsulated electrophoresis and other electro-optical media. Such encapsulated media contain numerous small capsules, each containing an inner phase with electrophoretically mobile particles in a liquid, and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held within a polymeric binder to form an adhesion layer located between two electrodes. The techniques described in these patents and applications include: (a) Electrophoretic particles, fluids and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814; (b) Capsules, binders and encapsulation processes; see, for example, U.S. Patent Nos. 6,922,276 and 7,411,719; (c) Films and subassemblies containing electro-optical materials, see, for example, U.S. Patent Nos. 6,982,178 and 7,839,564; (d) Backplanes, adhesive layers and other auxiliary layers and methods used in displays, for example, U.S. Patent Nos. D485,294, 6,124,851, 6,130,773, 6,177,921, 6,232,950, 6,252,564, 6,312,304, 6,312,971, 6,376,828, 6,392,786, 6,413,790, 6,422,687, 6,445,374, 6,480,182, 6,498,114, No. 6,506,438, No. 6,518,949, No. 6,521,489, No. 6,535,197, No. 6,545,291 , No. 6,639,578, No. 6,657,772, No. 6,664,944, No. 6,680,725, No. 6,683,3 No. 33, No. 6,724,519, No. 6,750,473, No. 6,816,147, No. 6,819,471, No. 6,82 No. 5,068, No. 6,831,769, No. 6,842,167, No. 6,842,279, No. 6,842,657, No. 6, 865,010, 6,967,640, 6,980,196, 7,012,735, 7,030,412, No. 7,075,703, No. 7,106,296, No. 7,110,163, No. 7,116,318, No. 7,148,128 No. 7,167,155, No. 7,173,752, No. 7,176,880, No. 7,190,008, No. 7,206, No. 119, No. 7,223,672, No. 7,230,751, No. 7,256,766, No. 7,259,744, No. 7,28 No. 0,094, No. 7,327,511, No. 7,349,148, No. 7,352,353, No. 7,365,394, No. 7 ,365,733, 7,382,363, 7,388,572, 7,442,587, 7,492,497, No. 7,535,624, No. 7,551,346, No. 7,554,712, No. 7,583,427, No. 7,598,17 No. 3, No. 7,605,799, No. 7,636,191, No. 7,649,674, No. 7,667,886, No. 7,672,No. 040, No. 7,688,497, No. 7,733,335, No. 7,785,988, No. 7,843,626, No. 7,859,637, No. 7,893,435, No. 7,89 No. 8,717, No. 7,957,053, No. 7,986,450, No. 8,009,344, No. 8,027,081, No. 8,049,947, No. 8,077,141, No. 8,0 U.S. Patent Publications No. 89,453, No. 8,208,193, No. 8,373,211, No. 9,726,957, No. 10,520,786, No. 10,585,325, and No. 11,513,414, as well as U.S. Patent Application Publications 2002 / 0060321, 2004 / 0105036, 2005 / 0122306, 2005 / 0122563, and 2007 / 00527 No. 57, No. 2007 / 0097489, No. 2007 / 0109219, No. 2007 / 0211002, No. 2009 / 0122389, No. 2009 / 0315044, No. 201 No. 0 / 0265239, No. 2011 / 0026101, No. 2011 / 0140744, No. 2011 / 0187683, No. 2011 / 0187689, No. 2011 / 0286082 See also Patent Nos. 2011 / 0286086, 2011 / 0292319, 2011 / 0292493, 2011 / 0292494, 2011 / 0297309, 2011 / 0310459, and 2012 / 0182599, as well as International Publication No. WO00 / 38000; see European Patent Nos. 1,099,207B1 and 1,145,072B1; (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; (f) Methods for driving a display; see, for example, U.S. Patent Nos. 7,012,600, 7,119,772, 7,453,445, and 10,475,396; (g) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348; (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.

[0012] 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, and that thus the electrophoretic medium can produce a so-called polymer-dispersed electrophoretic display comprising multiple discrete droplets of the electrophoretic medium and a continuous phase of polymer material, and that discrete droplets of the electrophoretic medium in such a polymer-dispersed electrophoretic display can be considered capsules or microcapsules even if the discrete capsule membrane is not associated with each individual droplet, see, for example, U.S. Patent No. 6,866,760. For the purposes of this application, such polymer-dispersed electrophoretic media are considered a variant of encapsulated electrophoretic media.

[0013] The type of electrophoretic display in question is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, charged pigment particles and fluids are not encapsulated within microcapsules, but rather are deposited within multiple voids formed in a carrier medium, typically a polymer film. See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, Inc.

[0014] Electrophoretic media are often opaque (for example, in many electrophoretic media, particles substantially block the transmission of visible light through the display) and operate in reflective mode; however, many electrophoretic displays can be configured to operate in a so-called "shutter mode," where one display state is substantially opaque and the other is light-transmitting. 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 displays, which are similar to electrophoretic displays but rely on variations in electric field intensity, can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optical displays may also be able to operate in shutter mode. An electro-optical medium operating in shutter mode may be useful in a multilayer structure for a full-color display, in which at least one layer adjacent to the screen of the display operates in shutter mode to expose or hide a second layer further away from the screen.

[0015] Encapsulated electrophoretic displays typically do not suffer from the clustering and sedimentation failure modes of traditional electrophoretic devices and offer further advantages, such as the ability to print or coat displays on a wide variety of flexible and rigid substrates. The use of the term “printing” is intended to include all forms of printing and coating, including but not limited to pre-metrized coatings, such as patch-die coatings, slot or extrusion coatings, slide or cascade coatings, curtain coatings; roll coatings, such as knife-over roll coatings, forward and reverse roll coatings; gravure coatings; immersion coatings; spray coatings; meniscus coatings; spin coatings; brush coatings; air knife coatings; silkscreen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques. Thus, the resulting displays can be flexible. Furthermore, since the display medium can be printed using a variety of methods, the displays themselves can be manufactured inexpensively.

[0016] An electro-optic display typically includes a layer of electro-optic material and at least two other layers positioned on either side of the electro-optic material, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define pixels on the display. For example, one electrode layer may be patterned into elongated row electrodes, and the other into elongated column electrodes running perpendicular to the row electrodes, with pixels defined by the intersections of the row and column electrodes. Alternatively, more commonly, one electrode layer may have the form of a single continuous electrode, and the other electrode layer may be patterned into a matrix of pixel electrodes, each defining one pixel on the display. In another type of electro-optic display intended for use with a stylus pen, print head, or similar movable electrode separate from the display, only one of the layers adjacent to the electro-optic layer contains electrodes, and the layer opposite the electro-optic layer is typically a protective layer, intended to prevent the movable electrode from damaging the electro-optic layer.

[0017] The manufacture of a three-layer electro-optical display typically involves at least one lamination operation. For example, some of the aforementioned MIT and E Ink patents and applications describe a process for manufacturing an encapsulated electrophoretic display, in which an encapsulated electrophoretic medium containing capsules in a binder is coated onto a flexible substrate containing an indium tin oxide (ITO) or similar conductive coating (acting as one electrode in the final display) on a plastic film, and the capsule / binder coating is dried to form an adhesion layer of the electrophoretic medium firmly bonded to the substrate. Separately, a backplane is prepared containing an array of pixel electrodes and a suitable arrangement of conductors for connecting to the pixel electrodes and driving the circuit. To form the final display, the substrate having the capsule / binder layer thereon is laminated onto the backplane using a lamination adhesive. (Using a very similar process, electrophoretic displays can be prepared for use with a stylus pen or similar movable electrode by replacing the backplane with a simple protective layer, such as a plastic film, on which a stylus pen or other movable electrode can slide.) In one preferred form of such a process, the backplane itself is flexible and is prepared by printing the pixel electrodes and conductors onto a plastic film or other flexible substrate. An obvious lamination technique for mass production of displays by this process is roll lamination using a lamination adhesive. Similar manufacturing techniques may be used in other types of electro-optical displays. For example, a microcell electrophoretic medium or a rotational dichroic component medium may be laminated onto the backplane in substantially the same manner as the encapsulated electrophoretic medium.

[0018] As discussed in the aforementioned U.S. Patent No. 6,982,178 (see column 3, line 63 to column 5, line 46), many of the components used in solid-state electro-optical displays and the methods used to manufacture such displays are derived from the techniques used in liquid crystal displays (LCDs), which are also electro-optical displays, although they use liquids rather than solid media. For example, a solid-state electro-optical display can utilize an active matrix backplane containing an array of transistors or diodes and a corresponding array of pixel electrodes, as well as "continuous" front electrodes on a transparent substrate (meaning electrodes that extend across multiple pixels and typically the entire display), and these components are essentially the same as those of an LCD. However, the methods used to assemble an LCD cannot be used for a solid-state electro-optical display. An LCD is typically assembled by forming the backplane and front electrodes on separate glass substrates, then bonding these components together with a small opening between them, placing the resulting assembly under vacuum, and immersing the assembly in a liquid crystal bath so that the liquid crystal flows through the opening between the backplane and the front electrodes. Finally, the liquid crystal is placed in place and the opening is sealed to provide the final display.

[0019] This LCD assembly process cannot be easily transferred to solid-state electro-optic displays. Because the electro-optic material is solid, it must exist between the backplane and the front electrode before these two integers are fixed to each other. Furthermore, in contrast to liquid crystal materials, which are simply placed between the front electrode and the backplane without being attached to either, the solid-state electro-optic medium typically needs to be fixed to both, and in most cases, the solid-state electro-optic medium is formed on the front electrode because this is generally easier than forming the medium on the circuit-containing backplane. Then, typically, the entire surface of the electro-optic medium is covered with adhesive and the front electrode / electro-optic medium combination is laminated onto the backplane by lamination under heat, pressure, and possibly vacuum. Therefore, most prior art methods for the final lamination of solid-state electrophoretic displays are essentially batch methods in which the electro-optic medium, lamination adhesive, and backplane are joined immediately before the final assembly, and it is desirable to provide a method that is better suited to mass production.

[0020] The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling solid-state electro-optic displays (including encapsulated electrophoretic displays) that are well-suited for mass production. Essentially, this patent describes a so-called “front-plane laminate” (“FPL”) comprising, in order, a light-transmitting conductive layer, a layer of solid-state electro-optic medium in electrical contact with the conductive layer, an adhesive layer, and a release sheet. Typically, the light-transmitting conductive layer is supported on a light-transmitting substrate, which is preferably flexible in the sense that the substrate can be manually wound around a drum (for example) with a diameter of 10 inches (254 mm) without permanent deformation. The term “light transmittance” as used in this patent and herein means that a layer designated in this way transmits enough light to allow an observer looking into the layer to observe changes in the display state of an electro-optic medium, which would typically be seen through the conductive layer and adjacent substrates (if any). If the electro-optic medium displays changes in reflectivity at invisible wavelengths, the term “light transmittance” should naturally be interpreted as referring to the transmission of the invisible wavelengths in question. The substrate is typically a polymer film, typically having 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 conveniently a thin metal or metal oxide layer, for example, 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 EIdu Pont de Nemours & Company, Wilmington DE, as "aluminum-treated Mylar" ("Mylar" is a registered trademark), and such commercially available materials can be used with good results in front-plane laminates.

[0021] The assembly of an electro-optical display using such a front-plane laminate may be achieved by removing the release liner from the front-plane laminate and bringing the adhesive layer into contact with the backplane under conditions effective for bonding the adhesive layer to the backplane, thereby fixing the adhesive layer, the electro-optical medium layer, and the conductive layer to the backplane. This process is well suited to mass production because the front-plane laminate can be mass-produced, typically using roll-to-roll coating techniques, and then cut into sections of any size required for use with a particular backplane.

[0022] U.S. Patent No. 7,561,324 describes a so-called “double release sheet,” which is essentially a simplified version of the front-plane laminate described in U.S. Patent No. 6,982,178. One form of the double release sheet includes a layer of solid electro-optical medium sandwiched between two adhesive layers, one or both of which are covered by the release sheet. Another form of the double release sheet includes a layer of solid electro-optical medium sandwiched between two release sheets. Both forms of the double release film are intended for use in a process generally similar to the process for assembling an electro-optical display from the front-plane laminate described above, but with two separate laminations, typically in the first lamination in which the double release sheet is laminated to the front electrodes to form a front subassembly, and then in the second lamination in which the front subassembly is laminated to the backplane to form the final display, although the order of these two laminations may be reversed if desired.

[0023] U.S. Patent No. 7,839,564 describes a so-called "reverse front-plane laminate," which is a variation of the front-plane laminate described in U.S. Patent No. 6,982,178. This reverse front-plane laminate comprises, in order, at least one of a light-transmitting protective layer and a light-transmitting conductive layer, an adhesive layer, a solid-state electro-optic medium layer, and a release liner. Using this reverse front-plane laminate, an electro-optic display is formed having a layer of laminate adhesive between the electro-optic layer and the front electrode or front substrate, wherein a second, typically thin, adhesive layer may or may not be present between the electro-optic layer and the backplane. Such an electro-optic display can combine good resolution with good low-temperature performance.

[0024] In high-resolution displays, each individual pixel must be addressable without interference from the addressing of neighboring pixels (regardless of whether the electro-optic medium used is bistable or not). One method to achieve this objective is to provide an array of nonlinear elements, such as transistors or diodes, where at least one nonlinear element is associated with each pixel to generate an active matrix display as described above. An addressing (pixel) electrode for addressing a single pixel is connected to a suitable voltage source through its associated nonlinear element. Conventionally, in high-resolution arrays, pixels are arranged in a two-dimensional array of rows and columns, so that any particular pixel is uniquely defined by the intersection of one identified row and one identified column. The sources of all transistors in each column are connected to a single column electrode, while the gates of all transistors in each row are connected to a single row electrode; the assignment of sources to rows and gates to columns is conventional and may be reversed if desired. Row electrodes are connected to row drivers, which essentially ensure that a voltage is applied to the selected row electrodes to ensure that only one row is selected at any given moment, i.e., that all transistors in the selected row are conductive, while voltages are applied to all other rows to ensure that all transistors in those unselected rows remain nonconductive. Column electrodes are connected to column drivers, which apply voltages to the various column electrodes to drive the pixels in the selected rows to their desired optical states. The aforementioned voltages are applied to common front electrodes, conventionally located on the opposite side of the electro-optical medium from the nonlinear array and extending across the entire display. After a pre-selected interval known as the "line address time," the voltages to the column drivers change so that the selected row is deselected, the next row is selected, and the next line of the display is written. This process is repeated so that the entire display is written in a row-by-row manner.

[0025] In the following discussion, the term “waveform” will be used to refer to the entire voltage curve over time used to realize a pixel transition from one particular initial gray level to a particular final gray level. Typically, such a waveform will contain multiple waveform components, where these components are essentially rectangular (i.e., where a given component involves the application of a constant voltage over a certain period of time), and these components may be called “pulses” or “driving pulses.” The term “driving scheme” refers to a set of waveforms sufficient to realize all possible transitions between gray levels for a particular display. A display may utilize more than one driving scheme; for example, U.S. Patent No. 7,012,600 teaches that a driving scheme may need to be modified depending on parameters such as the temperature of the display or the time it has been operating during its lifetime, and therefore a display may be provided with multiple different driving schemes to be used at different temperatures, etc. The set of driving schemes used in this scheme may be referred to as the “set of relevant driving schemes.”

[0026] Prior art front electrodes for use with electrophoresis and similar electro-optic displays typically consist of a very thin (about 0.1 μm) layer of ceramic, such as indium tin oxide or similar mixed metal oxides (see U.S. Patent No. 6,982,178 above). This thin layer is usually formed by sputtering the ceramic onto a polymer film, typically poly(ethylene terephthalate). Prior art back (pixel) electrodes may be formed in a similar manner or from a thin metal film. The front electrode must, of course, be light-transmitting so that the electro-optic layer is visible, whereas the back electrode can be opaque if the electro-optic layer is reflective.

[0027] Although ceramic front electrodes have been used commercially on a large scale for many years, they still suffer from several mechanical, optical, and electrical problems. The tension and temperature used during the lamination step in display manufacturing can cause the ceramic to crack, creating discontinuities in conductivity and leading to poor or inconsistent switching of the display. These cracks are also in areas with high water vapor permeability, which can cause localized damage to humidity-sensitive electro-optic media (many of the aforementioned types of electro-optic media are highly sensitive to humidity). In color displays using color filter arrays (CFAs), it is desirable to reduce parallax problems by using thin polymer films to bring the CFA as close as possible to the electro-optic layer and by reducing the thickness of the ITO-coated PET substrate. The thinner the PET substrate is fabricated, the greater the thermal shrinkage of the thinner substrate, which exacerbates the cracking challenges associated with ITO.

[0028] As discussed in detail in U.S. Patent No. 7,119,772, it has been found that for at least some types of electro-optical displays, the driving scheme at each pixel position is desirable to be DC-balanced in the sense that the algebraic sum of the impulses applied during any sequence of transitions that begin and end at the same gray level is bounded. It has been found that precisely DC-balanced waveforms (i.e., the integral of the current over time for any particular pixel of the display is kept at zero over the extended operating period of the display) are required to protect image stability, maintain symmetrical switching characteristics, and provide maximum useful operating life in certain displays of the prior art.

[0029] Generally, it is preferable that all individual waveforms within a drive scheme be DC balanced, but in practice, this is 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.

[0030] As discussed in U.S. Patent No. 7,119,772, the extent to which DC unbalanced drive affects electrophoresis or other electro-optical displays (estimated to be due to the polarization of certain display components, as will be discussed in more detail below) can be determined by measuring the open-circuit potential, which will hereafter be referred to as the "residual voltage" of a specific region of the display, such as a pixel. If the residual voltage of a pixel is zero, it is considered DC balanced. If the residual voltage is positive, it is considered DC unbalanced in the positive direction. If the residual voltage is negative, it is considered DC unbalanced in the negative direction. Non-zero residual voltages have been shown to correlate with difficulties in setting accurate gray levels.

[0031] The degradation of display performance caused by residual voltage generation is generally reversible, either by retracting the display without further switching or by properly switching to reequilibrium the DC impulse. However, if prior art electrophoretic displays are driven with extreme DC unequilibrium, the electrodes may be irreversibly degraded by electrochemical reactions that presumably consume the electrode material. While DC-balanced drive waveforms effectively protect against residual voltage and electrode degradation, their use presents problems. Additional time must be allocated to provide a balanced impulse, sometimes resulting in refresh times that are two to three times longer than those possible with unbalanced DC drive. In some electrophoretic compositions, the time required for the optical transition from black to white differs from the time required for the transition from white to black. With DC-balanced waveforms, the longer of the two switching times must be used for both transitions. Additionally, distracting optical transitions can become visible to the display user during DC-balanced refresh. For example, as described in U.S. Patents 6,724,519 and 7,564,614, corrosion inhibitors may be incorporated into electro-optic displays to prevent damage to electrodes from DC imbalance during display operation. U.S. Patents 9,726,957, 10,520,786 and 11,513,414 disclose electrophoretic displays having an electro-optic material containing an encapsulated electrophoretic medium and a polymer layer between the electro-optic material layer and the electrodes, wherein the polymer layer contains a redox compound. The redox material reduces the degradation of display components from DC imbalance. The present invention provides a more effective alternative method for preventing damage by including an organic electroactive compound in the electrophoretic medium. The present invention also provides an effective method for reducing the residual voltage of an electro-optic device. In the electro-optic device of the present invention, the electrophoretic medium is in direct contact with a first electrode and at least one pixel electrode of the device. Organic electroactive compounds exist in the electrophoretic medium in both oxidized and reduced forms. The reduced form is oxidizable at one of the electrodes, and the oxidized form is reducible at the other electrode, preventing damage to the device's electrodes and other components. [Prior art documents] [Patent Documents]

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[0034] Summary of the Invention Accordingly, the present invention provides an electro-optical device comprising a first electrode layer including a light-transmitting electrode, a second electrode layer including a plurality of pixel electrodes, and a microcell layer, wherein the microcell layer is disposed between the first electrode layer and the second electrode layer. The microcell layer comprises a plurality of microcells, each microcell containing an electrophoretic medium, the electrophoretic medium being in contact with the light-transmitting electrode of the first electrode layer and at least one 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 exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound is electrochemically reducible on one surface of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable on one surface of the first and second electrode layers. The oxidized and reduced forms of the organic electroactive compound are either (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) contained within the inverse micelle structure present in the electrophoretic medium. The oxidized form of the organic electroactive compound may have a reduction potential of 1.0 V or less compared to a standard hydrogen electrode.

[0035] The molecular structure of the reduced form of the organic electroactive compound can be represented by Formulas I to IX. R1 to R 39 may be hydrogen, a substituted or unsubstituted alkyl or aryl group, and the 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 may form a ring, and at least one of R 31 and R 32 is an aryl group, at least one of R 33 and R 34 is an aryl group, and at least one of R 36 and R 37 is an aryl group.

Chemical formula

Chemical formula

[0036] The groups R1 to R 39may be hydrogen, a substituted or unsubstituted alkyl, alkenyl, or aryl group. Substituents R1 and R2 (together), as well as / or R3 and R4, as well as / or R5 and R6, as well as / or R6 and R7, as well as / 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 R may form a ring. 31 and R 32 At least one of them may be an aryl group, R 33 and R 34 At least one of them is an aryl group, R 36 and R 37 At least one of them is an aryl group.

[0037] At least one of R1 to R4 in Equation I, at least one of R5 to R8 in Equation II, and R9 to R in Equation III 13 At least one of the R in equation IV 14 From R 18 At least one of the R of equation V 19 From R 24 At least one of the R values ​​in Equation VI 25 From R 30 At least one of the R in formula VII 31 and R 32 At least one of the R in equation VIII 33 From R 35 At least one of the following, as well as R of formula IX36 From R 39 At least one of these may be an alkyl or alkenyl group having at least 10 carbon atoms.

[0038] From R9 in Equation III to R 12 At least one of the R in equation IV 14 From R 17 At least one of the R of equation V 19 From R 22 At least one of the R values ​​in Equation VI 25 From R 28 At least one of the R in equation VIII 33 and R 34 At least one of the following, as well as R of formula IX 36 and R 37 At least one of the groups may be an alkyl or alkenyl group having at least 10 carbon atoms. The alkyl or alkenyl group may have between 10 and 100 carbon atoms. The alkyl or alkenyl group may include an isoprene dimer or oligomer containing 1 to 20 isoprene units (-CH2CH=C(CH3)CH2-). The alkyl or alkenyl group may include an isoprene dimer or oligomer containing 1 to 13 isoprene units (-CH2CH=C(CH3)CH2-).

[0039] The molecular structure of the reduced form of an organic electroactive compound may be represented by formula X. Groups R1, R2, and R3 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and n may be an integer from 2 to 20. Groups R1 and R2 may both be methoxy groups, and R3 may be a methyl group. Groups R1 and R2 may both be methyl groups, and R3 may be hydrogen. [ka]

[0040] The reduced form of the organic electroactive compound may be ubiquinol-10. [ka]

[0041] The reduced form of the organic electroactive compound can be represented by formula XI [Chemical formula] as follows.

[0042] The molecular structure of the oxidized form of the organic electroactive compound can be represented by formula XII. The groups R 40 , R 41 , R 42 , R 43 , and R 44 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and m may be an integer from 2 to 20. [Chemical formula]

[0043] The molecular structure of the oxidized form of the organic electroactive compound can be represented by formula XIII or formula XIV. The groups R 45 , R 46 , R 47 , R 48 , R 49 , R 50 , R 51 , and R 52 may be hydrogen, alkyl, alkenyl, or alkoxy groups, p may be an integer from 2 to 20, and q may be an integer from 2 to 20. The integer q can be selected from the group consisting of 3, 4, 7, and 9.

[0044] When the organic electroactive compound is represented by formula XIV, the groups R 48 , R 49 , R 50 , and R 51 may all be hydrogen, and R 52 may be methyl. [Chemical formula] [ka]

[0045] In another embodiment, the present invention provides a method for operating an electro-optical device, comprising the steps of (a) preparing the electro-optical device and (b) driving the electro-optical device using a DC unbalanced waveform. The residual voltage of the electro-optical device may be lower than the residual voltage of a reference electro-optical device, the reference electro-optical device comprising a reference electrophoretic medium that does not contain an organic electroactive compound. The electro-optical device comprises a first electrode layer comprising a light-transmitting electrode, a second electrode layer comprising a plurality of pixel electrodes, and a microcell layer, the microcell layer being positioned between the first electrode layer and the second electrode layer. The microcell layer comprises a plurality of microcells, each microcell comprising an electrophoretic medium, the electrophoretic medium being in contact with the light-transmitting electrode of the first electrode layer and at least one 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. Organic electroactive compounds exist in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of organic electroactive compounds is electrochemically reducible on one surface of the first and second electrode layers. The reduced form of organic electroactive compounds is electrochemically oxidizable on one surface of the first and second electrode layers. The oxidized and reduced forms of organic electroactive compounds are either soluble in the nonpolar liquid of the electrophoretic medium or contained in inverse micelle structures present in the electrophoretic medium.

[0046] In another embodiment, the present invention provides an electro-optical device comprising a first electrode layer including a light-transmitting electrode, a second electrode layer including a plurality of pixel electrodes, and a microcell layer, wherein the microcell layer is disposed between the first electrode layer and the second electrode layer. The microcell layer comprises a plurality of microcells, each microcell containing an electrophoretic medium, the electrophoretic medium being in contact with the light-transmitting electrode of the first electrode layer and at least one 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 exists in the electrophoretic medium in an oxidized or reduced form. The oxidized form of the organic electroactive compound is electrochemically reducible on one surface of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable on one surface of the first and second electrode layers. The oxidized and reduced forms of the organic electroactive compound are either (i) soluble in the nonpolar liquid of the electrophoretic medium, or (ii) contained within the inverse micelle structure present in the electrophoretic medium. The oxidized form of the organic electroactive compound may have a reduction potential of 1.0 V or less compared to a standard hydrogen electrode. [Brief explanation of the drawing]

[0047] [Figure 1] Figure 1 is a side view of an electro-optical display containing an electrophoretic medium encapsulated in microcapsules, based on prior art.

[0048] [Figure 2] Figure 2 is a side view of an electro-optical display containing an electrophoretic medium encapsulated within a microcell, based on prior art.

[0049] [Figure 3A] Figure 3A is a simplified diagram of the movement of charged species present in the electrophoretic medium and adjacent layers of an electro-optical display in response to an electric field that can lead to charge accumulation at the electrode interface and a reduction in display image quality. This figure is disclosed in the prior art.

[0050] [Figure 3B] Figure 3B is a simplified diagram of the movement and transformation of key species present in the electrophoretic medium and adjacent layers of an electro-optical display in response to an electric field. This diagram is disclosed in the prior art and relates to charge accumulation and residual voltage reduction at the electrode interface.

[0051] [Figure 4] Figure 4 is a side view of an example of an electro-optical device according to the present invention.

[0052] [Figure 5] Figure 5 shows a scheme of a redox reaction involving an organic electroactive compound.

[0053] [Figure 6] Figure 6 shows the oxidized and reduced forms of ubiquinol-10, as well as the redox reactions involved in the conversion between these two forms.

[0054] [Figure 7] Figure 7 shows the scheme of the redox reaction in the initial electrophoretic medium when the reduced form of an organic electroactive compound is introduced.

[0055] [Figure 8] Figure 8 is a graph of current versus time flowing through the electrophoretic medium of the present invention (which does not contain charged pigment particles) over 48 hours while a DC voltage is continuously applied across the liquid.

[0056] [Figure 9] Figure 9 is a graph of residual voltage versus time measured across the electrophoretic medium of the present invention, which does not contain charged pigment particles, after applying and removing a DC voltage across the liquid for 48 hours.

[0057] [Figure 10]Figure 10 is a graph of the measured current versus applied voltage flowing through the control and the electrophoretic media of the present invention, after driving and removing the applied voltage of the media using various DC voltages.

[0058] [Figure 11] Figure 11 is a graph of the measured residual voltage versus time through the control and the electrophoretic media of the present invention, after driving and removing the DC voltages used in the media.

[0059] [Figure 12] Figure 12 shows the waveform applied to the electro-optical device medium to measure the color gamut of the corresponding electrophoretic medium.

[0060] [Figure 13] Figure 13 shows the measured color gamut of a reference electro-optical device.

[0061] [Figure 14] Figure 14 shows the measured color gamut of the electro-optical device of the present invention. [Modes for carrying out the invention]

[0062] Detailed description of the invention The term “oxidized form” used herein in reference to organic electroactive compounds is used to include the fully oxidized form of an organic electroactive compound and other molecules that are more oxidized than the fully reduced form of an organic electroactive compound. The term “reduced form” used herein in reference to organic electroactive compounds is used to include the fully reduced form of an organic electroactive compound and other compounds that are more reduced than the fully oxidized form of an organic electroactive compound.

[0063] The term "unsubstituted alkyl group" refers to branched and unbranched groups that contain one or more single CC bonds but no double or triple CC bonds. The term "unsubstituted alkyl group" includes cyclic groups that contain single CC bonds but no double or triple CC bonds or aromatic groups. The term "unsubstituted alkenyl group" refers to branched and unbranched groups that contain one or more double CC bonds. The term "unsubstituted aryl group" refers to a group that contains an aromatic ring. The term "substituted alkyl group" refers to an alkyl group in which one or more hydrogens are replaced by a substituent, and the substituent is not an alkyl group. The substituent may be an alkenyl group, an aryl group, or a group containing a heteroatom, and the heteroatom is an atom from groups V to VII of the periodic table. The term "substituted alkenyl" refers to an alkenyl group in which one or more hydrogens are replaced by a substituent, and the substituent is neither an alkenyl group nor an alkyl group. Substituents may be aryl groups or groups containing heteroatoms, the heteroatoms being atoms from groups V to VII of the periodic table. The term "substituted aryl" refers to an aryl group in which one or more hydrogens are replaced by a substituent. Substituents may be alkyl groups, alkenyl groups, aryl groups, or groups containing heteroatoms, the heteroatoms being atoms from groups V to 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, carboxy, thio, cyano, nitro, and others.

[0064] A typical electro-optic display may have an electro-optic material layer containing 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 an example of a partial basic structure of an electro-optic display having microcapsules. The electro-optic display 100 includes a front plane 116, a back plane 118, and an adhesive layer 110 connecting the front plane 116 and the back plane 118. The front plane 116 includes a front substrate 102, a light-transmitting conductive layer 104 (also called the first electrode, top electrode, or common electrode in the literature), an optional polymer layer 106, and an electro-optic material layer 108. The back plane 118 includes a plurality of pixel electrodes 112 and a back substrate 114. The adhesive layer 110 connects the electro-optic material layer 108 of the front plane 116 to the back plane 118. The light-transmitting conductive layer 104 acts as the front electrode of the display. The electro-optic material layer 108 contains a plurality of microcapsules. Each microcapsule has a microcapsule wall and contains an electrophoretic medium having charged pigment particles in a nonpolar liquid. Typically, the plurality of microcapsules are deposited within a polymer binder. A viewer can see an image of the electrophoretic medium of the electro-optic display 100 from the side of the front substrate of the display.

[0065] Figure 2 is a side view of an example of a partial basic structure of an electro-optical display having microcells. The electro-optical display 200 has a viewing side 230 and includes a front substrate 202, a light-transmitting conductive layer 204, an electro-optical material layer 208, a sealing layer 209, and a backplane 218, the backplane including a plurality of pixel electrodes. The electro-optical material layer 208 includes a plurality of microcells 230A to D. Each microcell 230A to D of the electro-optical material layer 208 contains an electrophoretic medium 220. The electrophoretic medium 220 contains charged pigment particles 225 in a nonpolar liquid. Each microcell 230A to 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 covers each opening of the microcell and seals the electrophoretic medium 220 inside the microcell.

[0066] In the electro-optical display of Figure 1, which includes microcapsules, the front substrate 102 is light-transmitting. The front substrate 102 may be a plastic film, such as a sheet of poly(ethylene terephthalate) (PET), having a thickness of 25 to 200 μm. Although not shown in Figure 1, the front substrate 102 may further include one or more additional layers, such as a protective layer for absorbing ultraviolet radiation, a barrier layer for preventing oxygen or moisture from entering the display, and an anti-reflective coating for improving the optical properties of the display. The same applies to the electro-optical display of Figure 2, which includes microcells. That is, in the electro-optical display of Figure 2, which includes microcells, the front substrate 202 is light-transmitting. The front substrate 202 may be a plastic film, such as a sheet of poly(ethylene terephthalate) (PET), having a thickness of 25 to 200 μm. The front substrate 202 may further include one or more additional layers, such as a protective layer for absorbing ultraviolet radiation, a barrier layer for preventing oxygen or moisture from entering the display, and an anti-reflective coating for improving the optical properties of the display.

[0067] In the electro-optical display shown in Figure 1, which includes microcapsules, the light-transmitting conductive layer 104 may be a thin, continuous coating of a conductive material that minimizes the intrinsic absorption of electromagnetic radiation within the visible spectral range, for example, indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), graphene, etc. The same applies to the electro-optical display shown in Figure 2, which includes microcells. That is, the light-transmitting conductive layer 204 may be a thin, continuous coating of a conductive material that minimizes the intrinsic absorption of electromagnetic radiation within the visible spectral range, for example, indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), graphene, etc.

[0068] The electrophoretic media of the electro-optic display 100 in Figure 1 and the electrophoretic media of the electro-optic display 200 in Figure 2 may contain two types of charged pigment particles. The electrophoretic media of the displays may contain three, four, five, or more 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 media contains two types of charged pigment particles, i.e., a first and a second type of charged pigment particles, the first type of charged 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 via the light-transmitting conductive layer and the pixel electrodes of the backplane, the white particles of the electrophoretic medium move toward the positive electrode and the black particles move toward the negative electrode. Therefore, to an observer viewing the display from the viewing side (the front substrate side), the portion of the display corresponding to the pixel electrode appears either white or black, depending on whether the light-transmitting conductive layer is positive or negative relative to the pixel electrode.

[0069] As described in U.S. Patent No. 6,982,178, the adhesive layer 110 of the electrophoretic medium in the electro-optic display 100 is located between the electro-optic material layer 108 containing the encapsulated electrophoretic medium and the multiple pixel electrodes 112 of the backplane 118 (see Figure 1). The adhesive layer 110 enables the construction of the electro-optic display by joining two subassemblies, such as the frontplane 116 and backplane 118 in Figure 1. The adhesive layer 110 may be formed by coating an adhesive composition onto the surface of the electro-optic material layer 108, connecting the frontplane 116 and backplane 118, and then curing the adhesive composition thermally or via UV curing. In the case of the microcell electro-optic display in Figure 2, the sealing layer 209 is located between the multiple microcells containing the electrophoretic medium 220 and the pixel electrodes 212 of the backplane 218.

[0070] The adhesive layer 110 of the microcapsule electro-optic display 100 in Figure 1 and the sealing layer 209 of the microcell electro-optic display 200 in Figure 2 are located within an electrical circuit that separates the pixel electrodes of the backplane from the light-transmitting conductive layer. Therefore, the electrical properties of the adhesive layer of the microcapsule electro-optic display and the sealing layer of the microcell electro-optic display are important for the operation of the display and must be carefully adapted. For example, the sealing layer may contain conductive filler particles in addition to the polymer material to adjust its volume resistivity.

[0071] The polymer layer 106 of the microcapsule electro-optic display 100 in Figure 1 may be a laminated adhesive layer having similar properties to those described above with reference to the adhesive layer 110. However, because the polymer layer 106 is adjacent to the non-pixelated light-transmitting common electrode 104, its electrical conductivity may be higher than that of the laminated adhesive layer 110 adjacent to the pixelated backplane electrode 112, and if held at different potentials during display switching, it may not be conductive enough to lead to a significant current flowing from one backplane electrode to its adjacent one. If the polymer layer 106 is an adhesive layer, it may be used to bond the electro-optic material layer 108 to the electrode layer 104 during the manufacturing of the front plane, as described in detail in U.S. Patent No. 6,982,178 mentioned above.

[0072] Figure 3A is reproduced from prior art. Specifically, this figure was published as Figure 2 of U.S. Patent No. 9,726,957. It is a simplified illustration of the movement of charged species present in the electrophoretic media of the electro-optic material layer and adjacent layers of the electro-optic display 100 of Figure 1 in response to an electric field applied using 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 as will be obvious to those skilled in the art, other layers exist in the display. The mobile charged species within each layer are collectively referred to as positively charged species A, C, and E, and negatively charged species B, D, and F. Species A and B in the polymer layer 106 may arise, for example, from ionic dopants added to increase the conductivity of the polymer layer 106, or may be incidentally present in the material used to form the polymer layer 106. For example, if water is present in the polymer layer 106, species A may correspond to a proton produced by the ionization of water. Species A may contain more than one mobile cation species. In this discussion, species

[0073] Species A refers to any mobile, positively charged species within the polymer layer 106. Similarly, Species E and F refer to positively charged and negatively charged mobile species within the adhesive layer 110. Species C and D refer to mobile charged entities within the electrophoretic medium of the electro-optic material layer 108, such entities including charged pigment particles whose motion alters the optical state of the display, and charged species whose motion does not have a direct optical effect, such as micelle charges, which are well known in the art.

[0074] Charged species can cross the boundaries between the various layers of the display. This is schematically shown in Figure 3A, where a positively charged species E is shown crossing the boundary between the adhesive layer 110 and the electro-optic material layer 108. Furthermore, a negatively charged species B is shown crossing the boundary between the polymer layer 106 and the electro-optic material layer 108. If the charged entities are moved within their respective layers and cannot cross the interlayer boundaries, the charge will accumulate at the impermeable boundary and be stored, similar to how it is stored in an electrolytic capacitor. After removing the applied electric field and grounding electrodes 104 and 112, the charge stored at the boundaries within the display will discharge, changing the electric field experienced by the electrophoretic medium of the electro-optic material layer 108 and potentially altering the optical state of the display.

[0075] Even if mobile ionic charges can flow freely across interlayer boundaries within the display (without accumulating at internal boundaries), there remains the difficulty that ionic species cannot cross the boundaries between the inner layers of the display and electrodes 104 and 112. The only possible mechanism for charge transfer across these boundaries is electron transfer, i.e., reduction / oxidation chemical processes. If electron transfer between electrodes 104 and 112 and the inner layers is blocked, 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 in a DC unbalanced drive scheme, substantial charge accumulation can occur at these locations. The relaxation of accumulated charge when the electrodes are brought to a common potential can lead to a flow of charge carriers through the electro-optic material layer 108. This flow of charge carriers can lead to changes in the optical state of the display, which may be undesirable.

[0076] U.S. Patent No. 9,726,957, referred to above, discloses a technique for reducing the problem of charge accumulation by adding an electrochemically active compound to a layer of an electro-optical display adjacent to an electro-optical material layer. 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 published as FIG. 3 of the patent. As shown in FIG. 3B, charge accumulation at the electrode interface is reduced by an electrochemical oxidation / reduction reaction involving electron transfer from the electrode to the materials contained in the polymer layer 106 and the adhesive layer 110 of the electro-optical display of FIG. 1. At the cathode, electrons are transferred to reduce components in the adjacent layer (the reduction of neutral species G to provide anion G− is illustrated), while at the anode, electrons are transferred to the electrode, resulting in the oxidation of components in the adjacent layer (electron transfer from neutral species J to generate cation J+ is shown). The injected charge has a sign opposite to that of the charge moved during the initial polarization of the display, and thus, the accumulation of charge at the electrode interface is reduced. As shown in FIG. 3B, when a potential is applied to the electro-optical display 100 of FIG. 1, the movement of ions towards the electrode leads to the accumulation of charge in a thin diffusion layer near the electrode, and the thickness of these layers is on the order of the Debye screening distance, as is well known in the field of electrochemistry. Within these diffusion layers, the electrical potential gradient is very steep. After a certain time, the potential gradient becomes sufficient to cause an electron transfer reaction. The ease of electron transfer is determined, inter alia, by the redox potentials of the materials present near the electrode and their concentrations.

[0077] As mentioned above, in U.S. Patent No. 9,726,957, the electrochemically active compound used to control charge injection at the electrode interface is incorporated into a layer of the outer phase of the display, i.e., a layer separate from the electro-optic material layer containing the electrophoretic medium. However, in practice, it has been found that only components within a sufficiently short distance from effective electron transfer to or from the electrode will be effectively oxidized or reduced. Therefore, components undergoing electron transfer at the electrode may be depleted faster than the time required to be replenished by diffusion to the electrode surface, considering that the diffusion of typical electroactive compounds through polymers is too slow to sustain a practical current in the display. For this reason, the electro-optic device structure disclosed in U.S. Patent No. 9,726,957 is not optimal for mitigating the problems of charge accumulation at the electrode and the resulting residual voltage.

[0078] The inventors of the present invention have surprisingly found that a microcell electro-optic device having an electrophoretic medium in contact with at least one of a first electrode layer and a plurality of pixel electrodes, wherein the electrophoretic material comprises an organic electroactive compound, provides an effective reduction of residual voltage after long-term 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 the present invention comprises (1) a first electrode layer comprising a light-transmissive electrode, (2) a second electrode layer comprising a plurality of pixel electrodes, and (3) a microcell layer disposed between the first electrode layer and the second electrode layer. The microcell layer comprises a plurality of microcells, each microcell of the plurality of microcells comprises an electrophoretic medium, and the electrophoretic medium is in contact with at least one (or more than one or all of the pixel electrodes of the second electrode layer) of the light-transmissive 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 an oxidized form and a reduced form in the electrophoretic medium. The oxidized form of the organic electroactive compound is electrochemically reducible at the surface of one of the light-transmissive electrode of the first electrode layer and the pixel electrodes of the second electrode layer. The reduced form of the organic electroactive compound is electrochemically oxidizable at the surface of one of the light-transmissive electrode of the first electrode layer and the pixel electrodes of the second electrode layer. The oxidized form and the reduced form of the organic electroactive compound are soluble in the nonpolar liquid of the electrophoretic medium. Alternatively, the oxidized form and the reduced form of the organic electroactive compound are included in an inverse micelle structure present in the electrophoretic medium.

[0079] The content of organic electroactive compounds in the electrophoretic medium may be 0.1 to 10 weight percent based on the weight of the electrophoretic medium. The content of organic electroactive compounds in the electrophoretic medium may be 0.2 to 8 weight percent, 0.3 to 6 weight percent, 0.4 to 5 weight percent, 0.5 to 4 weight percent, 0.6 to 3 weight percent, or 0.7 to 2 weight percent based on the weight of the electrophoretic medium.

[0080] An inverse micelle structure in a nonpolar liquid (first liquid) is a droplet of a second liquid or a dispersion (particles in a third liquid) surrounded by amphiphilic molecules. The droplet forms the core of the inverse micelle structure. Amphiphilic molecules are molecules that have both hydrophobic groups (head) and hydrophobic groups (tail) in their molecular structure. Typically, the head of the amphiphilic molecule is oriented towards the core of each inverse micelle structure, and the tail is oriented towards the outer surface of the inverse micelle structure because the tail is hydrophobic and therefore more compatible with the nonpolar liquid. The second or third liquid is less hydrophobic than the tail of the amphiphilic molecule and the nonpolar fluid, and therefore more compatible with the head of the amphiphilic molecule. The nonpolar liquid is called the "continuous phase" of the inverse micelle / nonpolar liquid mixture.

[0081] Figure 4 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 to D. Each microcell 230A to D of the electro-optic material layer 208 contains an electrophoretic medium 320. The electrophoretic medium 320 contains charged pigment particles 225 in a nonpolar liquid. Microcell walls 232 separate adjacent microcells from each other. In the electro-optic device 300, at least one of the light-transmitting electrode of the first electrode layer 204 and one of the pixel electrodes 319 of the plurality of pixel electrodes of the second electrode layer 318 are in contact with the electrophoretic medium 320. More than one of the multiple pixel electrodes 319 of the second electrode layer 318 can be in contact with the electrophoretic medium. All of the multiple pixel electrodes 319 of 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, which includes circuits and a substrate. The fact that the electrophoretic medium is in contact with the light-transmitting electrodes of the first electrode layer and the pixel electrodes of the second electrode layer means that the electro-optic device 300 does not have to include a sealing layer that is present in commercially available microcell electro-optic displays containing electrophoretic medium.

[0082] The front substrate 202 of the electro-optical device 300 in Figure 4 may be a plastic film, such as a sheet of poly(ethylene terephthalate) (PET), having a thickness of 25 to 200 μm. The front substrate 202 may further include one or more additional layers, such as a protective layer for absorbing ultraviolet radiation, a barrier layer for preventing oxygen or moisture from entering the display, and an anti-reflective coating for improving the optical properties of the display.

[0083] The light-transmitting electrode of the first electrode layer 204 of the electro-optic device 300 in Figure 4 may be a thin, continuous coating of a conductive material that exhibits minimal intrinsic absorption of electromagnetic radiation within the visible spectral range, such as indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), graphene, etc.

[0084] The electrophoretic medium of the electro-optical display 300 in Figure 4 may contain two types of charged pigment particles. The electrophoretic medium of the display may contain three, four, five, or more 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 particles, i.e., first and second types of charged pigment particles, 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 via the light-transmitting electrode of the first electrode layer and the pixel electrode of the second electrode layer, the white particles of the electrophoretic medium move toward the positive electrode and the black particles move toward the negative electrode. Therefore, to an observer viewing the display from the viewing side (the side of the front substrate), the portion of the display corresponding to the pixel electrode appears either white or black, depending on whether the light-transmitting electrode is positive or negative relative to the pixel electrode.

[0085] The electrophoretic medium of the electro-optical display 300 in Figure 4 may further contain one or more charge control agents (CCAs). The CCAs may be low molecular weight surfactants, polymers, or blends of one or more components. The CCAs are used to stabilize or otherwise modify the sign and / or magnitude of the charge on charged pigment particles. CCAs are typically molecules 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. The CCAs are thought to form inverse micelle structures in the electrophoretic medium.

[0086] During the operation of an electro-optical device, organic electroactive compounds may exist in both oxidized and reduced forms in the electrophoretic medium. The oxidized form of the organic electroactive compound is electrochemically reducible at or near the surface of the light-transmitting electrode of the first electrode layer or the pixel electrode of the second electrode layer. The reduced form of the organic electroactive compound is electrochemically oxidizable at or near the surface of the light-transmitting electrode of the first electrode layer or the pixel electrode of the second electrode layer. That is, the oxidized form can be electrochemically reversibly reduced to the reduced form, and the reduced form can be electrochemically reversibly oxidized to the oxidized form. The conversion from the oxidized form to the reduced form and from the reduced form to the oxidized form is via a redox reaction. Therefore, electrochemically active organic compounds can also be called redox materials.

[0087] Organic electroactive compounds that can undergo at least partially reversible redox reactions are preferred over those that undergo irreversible reactions, but the ability to undergo completely 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 reduces premature degradation of the device and lowers the residual voltage over a period of time.

[0088] Figure 5 shows a scheme illustrating several key elements related to the operation of the electro-optic device of the present invention, including redox reactions at the electrodes. Figure 5 shows a cross-section of a microcell having two electrodes and an electrophoretic medium between the electrodes, the electrophoretic medium containing charged pigment particles and an organic electroactive compound. Typically, the distance between the electrodes is in the range of 5 to 25 μm. The electrophoretic fluid typically contains a nonpolar liquid with a low dielectric constant and charged pigment particles (P+ and P-). The symbols P+ and P- indicate that the electrophoretic medium contains positively charged pigment particles. In practice, the electrophoretic medium may contain more than two types of charged pigment particles having charge or varying sizes. Figure 5 also shows that the electrophoretic medium may contain charged inverse micelle structures M+ and M-. These inverse micelle structures may be formed from surfactant-like molecules such as CCA added to the electrophoretic medium to facilitate and maintain pigment charging. When a voltage is applied across a microcell via an electrode, positively charged pigment particles and positively charged inverse micelle structures move toward the more negatively charged electrode (hereinafter referred to as the cathode), while negatively charged pigment particles and negatively charged inverse micelle structures move toward the more positively charged electrode (hereinafter referred to as the anode). This movement of charge can shield the electric field experienced by either charged pigment particles or charged inverse micelle structures present in the portion of the electrophoretic medium away from the electrode. Thus, a potential gradient can be formed in the electrophoretic medium. That is, the potential may be higher near the electrode surface than in the space away from the electrode surface, because the movement of charged pigment particles and charged inverse micelle structures can enable electron transfer reactions involving the components of the electrophoretic medium.

[0089] The organic electroactive compound of the electrophoretic medium of the present invention is represented as Q (oxidized form) and QH2 (reduced form) in Figure 5. The oxidized form Q and reduced form QH2 of the organic electroactive compound form redox pairs in the electrophoretic medium. As shown in Figure 5, QH2 loses two electrons at the anode to form Q and two protons. At the cathode, Q gains two electrons and adds two protons to form the reduced form QH2. When 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, a current can be sustained. These redox reactions at the electrodes prevent depletion of the redox pair Q / QH2.

[0090] Electro-optical devices must be driveable in both directions. That is, the application of a voltage of one polarity should cause the movement of positively charged pigment particles toward the viewing side, and the application of a voltage of the opposite polarity should cause the movement of negatively charged pigment particles toward the viewing side. In this invention, regardless of which polarity is used to address the device, current can be sustained. That is, protons formed at the anode equilibrate with the negatively charged pigment particles and negatively charged inverse micelle structures driven at the anode, while protons are consumed at the cathode (or, in other words, an anionic material that consumes protons is formed at the cathode). Therefore, the electrochemical reaction at the electrodes can at least partially neutralize the charged pigment particles and charged inverse micelle structures that moved to the electrodes when the microcells were initially polarized. This charge neutralization can lead to a reduction in residual voltage that would otherwise cause electrical repulsion and image drift if the display were grounded after being driven. Since the current can be sustained indefinitely within the electro-optic device of the present invention, there is no reason to expect a substantial increase in residual voltage after initial polarization and the establishment of a steady state. In fact, the inventors have surprisingly found that, in a model system, the current can pass through a microcell containing the organic electroactive compound of the present invention for 48 hours without a substantial increase in residual voltage and without electrode degradation.

[0091] Any compound that (a) has oxidized and reduced forms that can be formed at least partially reversibly, and (b) is soluble in the nonpolar liquid of the electrophoretic medium, or can be part of an inverse micelle structure therein, can be used in the present invention. Preferred compounds include substituted quinone / hydroquinone pairs (or corresponding catechols) in which side reactions are minimized by preferred substitutions in one or more benzene rings. One particularly preferred compound pair is ubiquinol / ubiquinone, having the structure shown in Figure 6. Ubiquinol, the upper structure in Figure 6, is the reduced form, and ubiquinone, the lower structure in Figure 6, is the oxidized form.

[0092] The electrophoretic medium of the device can be initially charged in only one of two forms (oxidized or reduced form of the redox pair) because the corresponding partner compound will be formed when the device is driven. The reaction scheme for such formation is shown in Figure 7. Initially, when the device is driven, the reduced form QH2 of the organic electroactive compound initially present in the electrophoretic medium is converted to the oxidation of Q at the anode. Therefore, as shown in Figure 7, even if there is not enough Q at the cathode to sustain a current initially, another reduction, such as the reduction of a proton from water to form a hydrogen ion, may occur instead. This reaction does not have to be reversible. However, as this reaction proceeds at the cathode, more oxidized forms Q of the organic electroactive compound are generated and accumulate in the microcell until they reach a concentration sufficient to sustain a continuous current in the electrophoretic medium. Therefore, organic electroactive compounds may be added to the electrophoretic medium of the electro-optic device in either their reduced or oxidized forms, or a mixture of both forms. 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 may be used. In this case, it may be desirable that the standard reduction potential of the oxidized form of organic electroactive compound A is not more positive than that of the oxidized form of organic electroactive compound B. This can prevent reactions between the two organic electroactive compounds.

[0093] As mentioned above, the reduced form of the organic electroactive compound used in the present invention is oxidizable at the anode. However, it is preferable that this organic electroactive compound does not readily react with oxygen.

[0094] 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 39may be a hydrogen, substituted or unsubstituted alkyl, alkenyl, or aryl group, and the substituents R1 and R2, together with 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 may form a ring, and at least one of R 31 and R 32 is an aryl group, at least one of R 33 and R 34 is an aryl group, at least one of R 36 and R 37 is an aryl group.

[0095] At least one of R1 to R4 in formula I, at least one of R5 to R8 in formula II, at least one of R9 to R 13 in formula III, at least one of R 14 to R 18 in formula IV, at least one of R 19 to R 24 in formula V, at least one of R 25 to R 30 in formula VI, at least one of R 31 and R 32 in formula VII, at least one of R 33 to R 35 in formula VIII, and R in formula IX36 From R 39 At least one of these may be an alkyl or alkenyl group having at least 10 carbon atoms.

[0096] From R9 in Equation III to R 12 At least one of the R in equation IV 14 From R 17 At least one of the R of equation V 19 From R 22 At least one of the R values ​​in Equation VI 25 From R 28 At least one of the R in equation VIII 33 and R 34 At least one of the following, as well as R of formula IX 36 and R 37 At least one of the groups may be an alkyl or alkenyl group having at least 10 carbon atoms. The alkyl or alkenyl group may have between 10 and 100 carbon atoms. The alkyl or alkenyl group may contain an isoprene dimer or oligomer containing 1 to 20 isoprene units (-CH2CH=C(CH3)CH2-). The alkyl or alkenyl group may contain an isoprene dimer or oligomer containing 1 to 13 isoprene units (-CH2CH=C(CH3)CH2-).

[0097] The molecular structure of the reduced form of an organic electroactive compound may be represented by formula X. Groups R1, R2, and R3 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and n may be an integer from 2 to 20. Groups R1 and R2 may both be methoxy groups, and R3 may be a methyl group. Groups R1 and R2 may both be methyl groups, and R3 may be hydrogen.

[0098] The reduced form of an organic electroactive compound may be ubiquinol-10. The reduced form of an organic electroactive compound can be represented by formula XI.

[0099] The molecular structure of the oxidized form of an organic electroactive compound can be represented by formula XII. (R group)40 , R 41 , R 42 , R 43 , and R 44 may be a hydrogen, alkyl, alkenyl, or alkoxy group, and m may be an integer from 2 to 20.

[0100] The molecular structure of the oxidized form of the organic electroactive compound can be represented by Formula XIII or Formula XIV. The groups R 40 , R 41 , R 42 , R 43 , and R 44 may be a hydrogen, alkyl, alkenyl, or alkoxy group, p may be an integer from 2 to 20, and q may be an integer from 2 to 20. The integer q can be selected from the group consisting of 3, 4, 7, and 9. When the organic electroactive compound is represented by Formula XIV, the groups R 48 , R 49 , R 53 , R 50 , and R 51 may be hydrogen, and R 52 may be methyl.

[0101] The oxidized form of the organic electroactive compound may have a reduction potential of 1.0 V or less compared to the standard hydrogen electrode. Preferably, the oxidized form of the organic electroactive compound has a reduction potential of 0.2 V or less compared to the standard hydrogen electrode. There are organic electroactive compounds that meet this reduction potential criterion, and the organic electroactive compounds are soluble in the nonpolar liquid of the electrophoretic medium, so they can rapidly diffuse through the electrophoretic medium and participate in the electrochemical reaction at the electrode, reducing the residual voltage observed after long-term DC unbalanced driving.

[0102] While the present invention is by no means limited by this idea, it is conceivable that oxidation of water to form oxygen (a half-cell reaction at a standard reduction potential of over 1V) may occur in the absence of the organic electroactive compound according to the present invention. Since the organic electroactive compound used in the present invention is reduced more easily than water, the presence of such an organic electroactive compound reduces the ionic polarization required to generate a sufficiently steep potential gradient in the electrode bilayer for electron transfer, resulting in a lower residual voltage experienced by the electro-optic material.

[0103] As mentioned above, the use of organic electroactive compounds according to the present invention is intended to control the accumulation of charge 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 in order to enable DC unbalanced driving of displays without suffering irreversible electrode damage. The organic electroactive compounds of the present invention introduce competitive redox pathways to cause Faraday reactions at the electrode interface without electrode degradation. Without the use of organic electroactive compounds according to the present invention, unwanted Faraday reactions such as the electrolysis of water may occur, leading to the formation of byproducts such as hydrogen and oxygen gases. Even worse, the electrode material itself may be involved in redox reactions. Some materials used in transparent electrodes are easily oxidized. For example, silver metal nanowires or grids can easily oxidize to silver cations. Other materials widely used in transparent electrodes are easily reduced. For example, conductive polymers such as PEDOT:PSS lose their conductivity when reduced. Indium tin oxide (ITO), another common material used in transparent electrodes, can be irreversibly reduced to metallic tin or metallic indium, leading to discoloration (yellowing) of the transparent electrode and ultimately to complete failure. This invention seeks to introduce competitive redox chemistry to induce a Faraday reaction at the electrode interface without electrode degradation. In the case of ITO electrodes, it is desirable that the oxidation form of the organic electroactive compound used in this invention is reduced more readily than ITO. That is, selective reduction of the organic electroactive compound protects the ITO electrode from irreversible electrochemical degradation. On the other hand, it is desirable that the oxidation form of the organic electroactive compound is not reduced too readily, but rather that the reduced form is thermally oxidized, unless such oxidation produces a new reduced form (i.e., a reduced form corresponding to the oxidation form).

[0104] The electro-optic device of the present invention may be operated by an operating method comprising the steps of (a) preparing the electro-optic device and (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 reference electro-optic device.

[0105] The reference electro-optic device is a device comprising a reference electrophoretic medium. The reference electrophoretic medium is similar to the electrophoretic medium of the present invention in its composition, but does not contain an organic electroactive compound. The electro-optic device of the present invention comprises a first electrode layer comprising a light-transmitting electrode, a second electrode layer comprising a plurality of pixel electrodes, and a microcell layer, the microcell layer being positioned between the first and second electrode layers. The microcell layer comprises a plurality of microcells, each microcell comprising an electrophoretic medium, the electrophoretic medium being in contact with the light-transmitting electrode of the first electrode layer and at least one 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 exists in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound is electrochemically reducible on the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable on one surface 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 within inverse micelle structures present in the electrophoretic medium. [Examples]

[0106] (Example 1)

[0107] A solution was prepared containing (a) 1 wt% of a charge control agent based on the weight of the solution, (b) 1 wt% of ubiquinol based on the weight of the solution, and (c) Isopar E. The charge control agent was prepared as described in Example 2 of U.S. Patent Application Publication No. 2020 / 0355978. Ubiquinol-10 was supplied by Biosynth, Staad, Switzerland. Each was coated with a transparent conductive coating of indium tin oxide (ITO) and placed at intervals of 25 μm, 6.5 cm. 2A solution was introduced into a cell containing two opposing glass plates with a surface area of ​​[surface area]. The cell was sealed using an epoxy composition and then driven with 15V DC at 25°C for 48 hours. The current passing through the cell was continuously measured during the driving period. After this time, the cell was driven at 0V for 50 milliseconds, then floated, and the residual voltage was measured.

[0108] The current flowing during a 48-hour drive period is shown in Figure 8. The graph in Figure 8 shows the measured current versus time. From this graph, it can be seen that only a slight decrease in current was observed during the 48-hour drive period. The cell remained transparent throughout the entire drive period, but the ITO degraded and turned yellow under the same conditions when a control solution was used, where the control solution contained only CCA in Isopar E (no organic electroactive compounds). The residual voltage in the float for 300 seconds after a short drive at 0V is shown in Figure 9, which is a graph of the residual voltage over time. In conclusion, it was shown that a continuous DC current could pass through the model composition (containing the organic electroactive compounds of the present invention) without degrading either the electrodes or the model composition itself.

[0109] (Example 2)

[0110] An electrophoretic medium was prepared containing a white pigment similar to pigment W1 in U.S. Patent No. 10,678,111, a magenta pigment similar to pigment M1, and a cyan pigment similar to C1. The yellow pigment was 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 the CCA of Example 1. The total amount of this CCA in the electrophoretic composition was 1.8% by weight based on the weight of the electrophoretic medium. The electrophoretic medium also contained 1% by weight of polydimethylsiloxane polymer (PDMS DMS-T72, supplied by Gelest Corporation, with a molecular weight of approximately 700,000) as an image stabilizer, based on the weight of the electrophoretic medium. The weight % content of each type of pigment particle based on the weight of the electrophoretic medium is shown in Table 1.

[0111] [Table 1]

[0112] (Example 3)

[0113] The electrophoretic medium from Example 2 was separated into two parts, 2A and 2B. The distance between the two electrodes was 10 μm, and the surface area was 1 cm². 2 Sample 2A was loaded into a cell similar to the one described above in Example 1, except that it contained a different material. Sample 3B was prepared by adding ubiquinol and ubiquinone (1% by weight of ubiquinol and 1% by weight of ubiquinol based on the weight of the electrophoresis medium) to Sample 2B. Ubiquinol and ubiquinone are available from AmBeed, IL, USA. Sample 3B was loaded into a cell (the same type of cell as the one loaded with Sample 2A). The cells containing Samples 2A and 3B were driven with DC voltages having amplitudes of 1, 5, 15, and 30 V. Each voltage was applied for 240 seconds, and then they were driven at 0 V for 100 milliseconds. The cells were then floated, while the residual voltage was measured. Figure 10 shows the measured currents for Samples 2A and 3B as a function of applied voltage, while Figure 11 shows the residual voltage measured during the final float state. (i) The current passing through sample 3B (containing an organic electroactive compound) is higher than the current passing through sample 2A (control), and (ii) the residual voltage measured in sample 3B (containing an organic electroactive compound) is lower than that measured in sample 2A (control). In other words, the electrophoretic medium containing an organic electroactive compound according to the present invention exhibits improved performance (lower residual voltage).

[0114] The color gamut of electro-optic devices prepared from the electrophoretic media of sample 2A (control) and sample 3B (invention) was also measured. The entire color gamut (i.e., the volume of all colors addressable by the device) was explored using the waveform in Figure 12, which is the voltage applied to the backplane relative to the frontplane. Although not a practical waveform for commercial displays, the waveform in Figure 12 was used for test purposes. The waveform is made up of a “dipole,” i.e., a pair of pulses of opposite polarity, and its duration and magnitude vary systematically as shown by the dark envelope in Figure 12. The voltages investigated 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 all voltage pairs (+,-), all pulse duration pairs were observed once. This was done in a manner in which a pulse duration pair in one dipole changed by exactly one value in the next dipole, and this value was adjacent in an ordered list of pulse duration values. Voltages were investigated in a similar manner. Thus, the waveforms were as smooth as possible in that consecutive dipoles were as similar to each other as possible. Reflectance spectra were obtained throughout the entire waveform (not just at its termination) and converted to CIEL*a*b* units. The color gamut observed from an electro-optic device containing a control electrophoretic medium is shown in Figure 13, and the color gamut observed from an electro-optic device containing the electrophoretic medium of the present invention is shown in Figure 14. From Figures 13 and 14, it can be seen that the color gamuts of the control and the device of the present invention are very similar. That is, the organic electroactive compounds of the present invention can be added to electrophoretic media in such a way that they do not significantly affect their electro-optic performance, but enable DC drive with reduced residual voltage accumulation.

[0115] term

[0116] Item 1: A first electrode layer including a light-transmitting electrode, A second electrode layer containing multiple pixel electrodes, A microcell layer is disposed between the first electrode layer and the second electrode layer. An electro-optical device including, The microcell layer comprises a plurality of microcells, each of the plurality of microcells comprises an electrophoretic medium, the electrophoretic medium is in contact with the light-transmitting electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer, and the electrophoretic medium is (a) Charged pigment particles, (b) non-polar liquid; (c) Charge control agent, and (d) Organic electroactive compounds Includes, Here, The aforementioned organic electroactive compound is present in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound is electrochemically reducible on one surface of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable on one surface 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) part of an inverse micelle structure present in the nonpolar liquid of the electrophoretic medium. Electro-optical devices.

[0117] Item 2: The molecular structure of the reduced form of the organic electroactive compound is one of formulas I to IX. [In the formula, R1 to R 39 is hydrogen, a substituted or unsubstituted alkyl, alkenyl, or aryl group, and substituents R1 and R2 together are, 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 It may form a ring, R 31 and R 32 At least one of them is an aryl group, R 33 and R 34 At least one of them is an aryl group, R 36 and R 37 At least one of them is an aryl group. The electro-optical device described in item 1, represented by [the specified symbol].

[0118] Item 3: At least one of R1 to R4 in Equation I, at least one of R5 to R8 in Equation II, and R9 to R in Equation III 13 At least one of the R in equation IV 14 From R 18 At least one of the R of equation V 19 From R 24 At least one of the R values ​​in Equation VI 25 From R 30 At least one of the R in formula VII 31 and R 32 At least one of the R in equation VIII 33 From R 35 At least one of the following, as well as R of formula IX 36 From R 39 The electro-optical device according to item 2, wherein at least one of the members is an alkyl or alkenyl group having at least 10 carbon atoms.

[0119] Item 4: From R9 in Equation III to R 12 At least one of the R in equation IV 14 From R 17 At least one of the R of equation V 19 From R22 At least one of the R values ​​in Equation VI 25 From R 28 At least one of the R in equation VIII 33 and R 34 At least one of the following, as well as R of formula IX 36 and R 37 The electro-optical device according to item 2, wherein at least one of the members is an alkyl or alkenyl group having at least 10 carbon atoms.

[0120] Item 5: The electro-optical device according to item 3 or 4, wherein the alkyl or alkenyl group has between 10 and 100 carbon atoms.

[0121] Item 6: The electro-optical device according to any one of items 2 to 5, wherein the alkyl or alkenyl group comprises an isoprene dimer or oligomer containing 1 to 20 isoprenyl units (-CH2CH=C(CH3)CH2-).

[0122] Item 7: An electro-optical device according to any one of items 2 to 5, wherein the alkyl or alkenyl group comprises an isoprene dimer or oligomer containing 1 to 13 isoprenyl units (-CH2CH=C(CH3)CH2-).

[0123] Item 8: The molecular structure of the reduced form of the organic electroactive compound is given by formula X [In the formula, R1, R2, and R3 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and n is an integer from 2 to 20.] An electro-optical device as described in any one of items 2 through 7, represented by the above.

[0124] Item 9: The electro-optical device according to Item 8, wherein R1 and R2 are methoxy groups and R3 is a methyl group.

[0125] Item 10: The electro-optical device according to Item 9, wherein the reduced form of the organic electroactive compound is ubiquinol-10.

[0126] Item 11: The electro-optical device according to item 8, wherein R1 and R2 are methyl groups and R3 is hydrogen.

[0127] Item 12: The reduced form of the organic electroactive compound is, The electro-optical device described in item 11, represented by [the specified symbol].

[0128] Item 13: The molecular structure of the oxidized form of the organic electroactive compound is, Formula XII [In the formula, R 40 , R 41 , R 42 , R 43 , and R 44 m may be a hydrogen, alkyl, alkenyl, or alkoxy group, and m is an integer from 2 to 20. The electro-optical device described in item 1, represented by [the specified symbol].

[0129] Item 14: The molecular structure of the oxidized form of the organic electroactive compound is of formula XIII or formula XIV [In the formula, R 45 , R 46 , R 47 , R 48 , R 49 , R 50 , R 51 , and R 52 [where p is an integer from 2 to 20, and q is an integer from 2 to 20] The electro-optical device described in item 1, represented by [the specified symbol].

[0130] Item 15: 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 is hydrogen, R 52 The electro-optical device described in item 14, wherein the compound is methyl.

[0131] Item 16: The electro-optical device according to Item 15, wherein q is selected from the group consisting of 3, 4, 7, and 9.

[0132] Item 17: The electro-optic device according to any one of items 1 to 16, wherein the oxidation form of the organic electroactive compound has a reduction potential of 1.0 V or less compared to a standard hydrogen electrode.

[0133] Item 18: A method for operating an electro-optical device, (a) The step of preparing the electro-optical device described in item 1, (b) The step of driving the electro-optic device using a DC unbalanced waveform How to operate it, including.

[0134] Item 19: A method for operating the electro-optic device according to Item 18, wherein the residual voltage of the electro-optic device is lower than the residual voltage of a control electro-optic device, and the control electro-optic device comprises a control electrophoretic medium that does not contain an organic electroactive compound.

[0135] Item 20: A first electrode layer including a light-transmitting electrode, A second electrode layer containing multiple pixel electrodes, A microcell layer is disposed between the first electrode layer and the second electrode layer. An electro-optical device including, The microcell layer comprises a plurality of microcells, each of the plurality of microcells comprises an electrophoretic medium, the electrophoretic medium is in contact with the light-transmitting electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer, and the electrophoretic medium is (a) Charged pigment particles, (b) non-polar liquid; (c) Charge control agent, and (d) Organic electroactive compounds Includes, Here, The organic electroactive compound is present in the electrophoretic medium in at least one of the oxidized or reduced forms. The oxidized form of the organic electroactive compound is electrochemically reducible on one surface of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable on one surface 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) part of an inverse micelle structure present in the nonpolar liquid of the electrophoretic medium. Electro-optical devices.

Claims

1. A first electrode layer including a light-transmitting electrode, A second electrode layer containing multiple pixel electrodes, A microcell layer disposed between the first electrode layer and the second electrode layer An electro-optical device including, The microcell layer comprises a plurality of microcells, each of the plurality of microcells comprises an electrophoretic medium, the electrophoretic medium is in contact with the light-transmitting electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer, and the electrophoretic medium is (a) Charged pigment particles, (b) a nonpolar liquid; (c) Charge control agent, and (d) Organic electroactive compounds Includes, Here, The aforementioned organic electroactive compound is present in the electrophoretic medium in both oxidized and reduced forms. The oxidized form of the organic electroactive compound is electrochemically reducible on one surface of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable on one surface 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) part of an inverse micelle structure present in the nonpolar liquid of the electrophoretic medium. Electro-optical devices.

2. The molecular structure of the reduced form of the aforementioned organic electroactive compound is given by formulas I to IX 【Chemistry 9】 [In the formula, R １ to R ３９ may be a hydrogen, substituted or unsubstituted alkyl, alkenyl, or aryl group, and the substituents R １ and R ２ (together), and / or R ３ and R ４ , and / or R ５ and R ６ , and / or R ６ and R ７ , and / or R ７ and R ８ , R ９ 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 may form a ring, and at least one of R ３１ and R ３２ is an aryl group, and at least one of R ３３ and R ３４ is an aryl group, and at least one of R ３６ and R ３７ is an aryl group]] The electro-optical device according to claim 1, as represented by [the specified method].

3. R in Equation I １ From R ４ At least one of the R in Equation II ５ From R ８ At least one of the R in formula III. ９ From R １３ At least one of the R of formula IV １４ From R １８ At least one of the R in equation V １９ From R ２４ At least one of the R of formula VI ２５ From R ３０ At least one of the R in equation VII ３１ and R ３２ At least one of the R in equation VIII ３３ From R ３５ At least one of the following, and R of formula IX ３６ From R ３９ The electro-optical device according to claim 2, wherein at least one of the members is an alkyl or alkenyl group having at least 10 carbon atoms.

4. R in Equation III ９ From R １２ At least one of the R of formula IV １４ From R １７ At least one of the R in equation V １９ From R ２２ At least one of the R of formula VI ２５ From R ２８ At least one of the R in equation VIII ３３ and R ３４ At least one of the following, and R of formula IX ３６ and R ３７ The electro-optical device according to claim 2, wherein at least one of the members is an alkyl or alkenyl group having at least 10 carbon atoms.

5. The electro-optical device according to claim 3, wherein the alkyl or alkenyl group has from 10 carbon atoms to 100 carbon atoms.

6. The alkyl or alkenyl group comprises 1 to 20 isoprenyl units (-CH ２ CH = C(CH ３ )CH ２ The electro-optical device according to claim 5, comprising an isoprene dimer or oligomer containing -).

7. The alkyl or alkenyl group comprises 1 to 13 isoprenyl units (-CH ２ CH = C(CH ３ )CH ２ The electro-optical device according to claim 5, comprising an isoprene dimer or oligomer containing -).

8. The molecular structure of the reduced form of the aforementioned organic electroactive compound is given by formula X 【Chemistry 10】 [In the formula, R １ , R ２ , and R ３ n may be a hydrogen, alkyl, alkenyl, or alkoxy group, and n is an integer from 2 to 20. The electro-optical device according to claim 6, as represented by [the specified method].

9. R １ and R ２ is a methoxy group, R ３ The electro-optical device according to claim 8, wherein the group is a methyl group.

10. The electro-optical device according to claim 9, wherein the reduced form of the organic electroactive compound is ubiquinol-10.

11. R １ and R ２ is a methyl group, R ３ The electro-optical device according to claim 8, wherein the hydrogen is hydrogen.

12. The reduced form of the aforementioned organic electroactive compound is, Formula XI 【Chemistry 11】 The electro-optical device according to claim 11, as represented by [the specified figure].

13. The molecular structure of the oxidized form of the aforementioned organic electroactive compound is, Formula XII 【Chemistry 12】 [In the formula, R ４０ , R ４１ , R ４２ , R ４３ , and R ４４ m may be a hydrogen, alkyl, alkenyl, or alkoxy group, and m is an integer from 2 to 20. The electro-optical device according to claim 1, as represented by [the specified method].

14. The molecular structure of the oxidized form of the aforementioned organic electroactive compound is formula XIII or formula XIV 【Chemistry 13】 [wherein, R ４５ , R ４６ , R ４７ , R ４８ , R ４９ , R ５０ , R ５１ , and R ５２ may be hydrogen, an alkyl, an alkenyl, or an alkoxy group, p is an integer from 2 to 20, and q is an integer from 2 to 20] The electro-optical device according to claim 1, as represented by [the specified method].

15. The molecular structure of the oxidized form of the organic electroactive compound is represented by Formula XIV, where R ４８ , R ４９ , R ５０ , R ５１ is hydrogen, and R ５２ is methyl. The electro-optical device according to claim 14.

16. The electro-optical device according to claim 15, wherein q is selected from the group consisting of 3, 4, 7, and 9.

17. The electro-optic device according to claim 1, wherein the oxidation state of the organic electroactive compound has a reduction potential of 1.0 V or less compared to a standard hydrogen electrode.

18. A method for operating an electro-optical device, The steps of preparing the electro-optical device described in claim 1, The steps include driving the electro-optic device using a DC unbalanced waveform and How to operate it, including.

19. A method for operating an electro-optical device according to claim 18, wherein the residual voltage of the electro-optical device is lower than the residual voltage of a control electro-optical device, and the control electro-optical device includes a control electrophoretic medium that does not contain an organic electroactive compound.

20. A first electrode layer including a light-transmitting electrode, A second electrode layer containing multiple pixel electrodes, A microcell layer disposed between the first electrode layer and the second electrode layer An electro-optical device including, The microcell layer comprises a plurality of microcells, each of the plurality of microcells comprises an electrophoretic medium, the electrophoretic medium is in contact with the light-transmitting electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer, and the electrophoretic medium is (a) Charged pigment particles, (b) a nonpolar liquid; (c) Charge control agent, and (d) Organic electroactive compounds Includes, Here, The organic electroactive compound is present in the electrophoretic medium in at least one of the oxidized or reduced forms. The oxidized form of the organic electroactive compound is electrochemically reducible on one surface of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable on one surface 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) part of an inverse micelle structure present in the nonpolar liquid of the electrophoretic medium. Electro-optical devices.

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