Color electro-optic displays comprising light resistant additives

Abstract

The present application discloses a color electro-optic display (100, 200, 300) comprising an electrophoretic medium (122, 222), the electrophoretic medium (122, 222) comprising different types of charged pigment particles (262, 272), at least one of the different types of charged pigment particles being an organic electrically active compound, a light resistance additive, and a non-polar liquid. The light resistant additive is an electron acceptor and improves the light resistance of a color electrophoretic display.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 546,536, filed on October 31, 2023, which, together with all other patents and patent applications disclosed herein, is incorporated herein by reference in its entirety. Background of the Invention

[0003] This invention relates to a color electro-optic display comprising an electro-optic material layer having an electrophoretic medium containing a lightfastness additive. The lightfastness additive improves the lightfastness of the color electro-optic display. The electrophoretic medium of the electro-optic material layer of the electro-optic display further contains charged particles in a non-polar liquid.

[0004] The terms “bistable” and “bistable” are used herein in their conventional sense in the art to refer to a display comprising display elements having a first display form and a second display form that are different in at least one optical property, such that after either given element has been driven to present its first or second display form by an addressing pulse of finite duration, the state will persist for at least several times, for example, at least four times, the minimum duration of the addressing pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of displaying grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, as are some other types of electro-optical displays. This type of display is aptly referred to as “multistable” rather than bistable; however, for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0005] When applied to materials or displays, the term "electro-optic" is used herein in its conventional meaning in the field of imaging to refer to a material having a first display state and a second display state that differ in at least one optical property, which is altered from its first display state to its second display state by applying an electric field to the material. While the optical property is typically color perceptible to the human eye, it can be another optical property, such as transmittance, reflectivity, luminescence, or, in the case of displays intended for machine reading, pseudocolor in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible light range.

[0006] Some electrophoretic media are solid in the sense that the material has a solid external surface, although the media may and often do have internal spaces filled with liquid or gas. For convenience, displays using solid electrophoretic media will be referred to as "solid-state electrophoretic displays" below.

[0007] Several types of electro-optic displays are known. One type of electro-optic display is the rotating bicolor unit type, as described in, for example, U.S. Patents Nos. 5,808,783; 5,777,782; 5,760,761; 6,054,071; 6,055,091; 6,097,531; 6,128,124; 6,137,467 and 6,147,791 (although this type of display is often referred to as a “rotating bicolor sphere” display, the term “rotating bicolor unit” is preferred because it is more accurate, since in some of the aforementioned patents the rotating unit is not spherical). Such a display uses a large number of small bodies (typically spherical or cylindrical) having two or more portions with different optical properties, as well as internal dipoles. These small bodies are suspended in liquid-filled vesicles within a matrix, allowing the small bodies to rotate freely. By applying an electric field to alter the appearance of the display, the volume is rotated to different positions, thus changing the portion of the volume seen through the viewing surface. This type of electro-optic medium is typically bistable.

[0008] Another type of electro-optic display uses an electrochromic medium, such as an electrochromic medium in the form of a nanochromic film, which comprises an electrode at least partially formed of a semiconductor metal oxide and a plurality of dye molecules capable of reversibly changing color attached to the electrode; see, for example, O'Regan, B. et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U. et al., Adv. Mater., 2002, 14(11), 845. This type of nanochromic film is also described, for example, in U.S. Patents 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.

[0009] Another type of electro-optic display is the electrowetting display developed by Philips and described in Hayes, R.A. et al., “Video-Speed ​​Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003). U.S. Patent No. 7,420,549 shows that such an electrowetting display can be fabricated to be bistable.

[0010] Electro-optic displays, a type of display that has been a key focus of research and development for many years, are particle-based electrophoretic displays, in which multiple charged particles move through a liquid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays offer advantages such as good brightness and contrast, wide viewing angles, bistable states, and low power consumption. However, long-term image quality issues have hindered their widespread application. For example, the particles constituting an electrophoretic display tend to settle, leading to a short lifespan for these displays.

[0011] A typical electrophoretic medium for an electrophoretic display contains at least one charge control agent (CCA). CCA controls the charge on the electrophoretic particles. Typically, CCA is a surfactant-like molecule with ionic or other polar groups (hereinafter referred to as head groups) and a nonpolar chain (usually a hydrocarbon chain, hereinafter referred to as the tail). CCA can recombine with or adsorb onto charged particles. It is believed that CCA forms reverse micelles in the electrophoretic medium, and it is this small fraction of charged reverse micelles that causes the conductivity in the medium. Reverse micelles contain a polar core, the size of which can vary from 1 nm to tens of nanometers, and can have spherical, cylindrical, or other geometries, surrounded by the nonpolar tail groups of the CCA molecule. In an electrophoretic medium, three phases can typically be distinguished: solid particles with surfaces, a highly polar phase distributed in the form of tiny droplets (reverse micelles), and a continuous phase containing a nonpolar fluid. When an electric field is applied, both the electrophoretic particles and the charged reverse micelles can move through the fluid, thus creating two parallel paths for conduction through the fluid (the fluid itself typically has a small conductivity approaching zero).

[0012] Numerous patents and applications assigned to or attributed to MIT and E Ink Corporation describe various techniques used in encapsulated electrophoretic media, as well as other electrophoretic media. Such encapsulated media comprise a plurality of microcapsules, each microcapsule comprising an inner phase and a capsule wall surrounding the inner phase, the inner phase containing electrophoretically mobile particles in a liquid. Typically, the microcapsules themselves are held in a polymer binder to form a coherent layer between two electrodes. The techniques described in these patents and applications include:

[0013] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patents 7,002,728 and 7,679,814;

[0014] (b) Microencapsulation, adhesives, and encapsulation processes; see, for example, U.S. Patents 6,922,276 and 7,411,719;

[0015] (c) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patents 6,982,178 and 7,839,564;

[0016] (d) Backplanes, adhesive layers, and other auxiliary layers and methods used in displays; see, for example, D485,294; 6,124,851; 6,130,773; 6,177,921; 6,232,950; 6,252,564; 6,312,304; 6,312,971; 6,376,828; 6,392,786; 6,413,790; 6,422,687; 6,445,374; 6,480,182; 6,498,114; 6,506 ,438;6,518,949;6,521,489;6,535,197;6,545,291;6,639,578;6,657,772;6,664,944;6,680,725;6,683,333;6,724,519;6,750,473;6,816,147;6,819,471;6,825,068;6,831,769;6,842,167;6,842,279;6,842,657;6,865,010;6, 967,640; 6,980,196; 7,012,735; 7,030,412; 7,075,703; 7,106,296; 7,110,163; 7,116,318; 7,148,128; 7,167,155; 7,173,752; 7,176,880; 7,190,008; 7,206,119; 7,223,672; 7,230,751; 7,256,766; 7,259,744; 7,280,094; 7,327,511 7,349,148; 7,352,353; 7,365,394; 7,365,733; 7,382,363; 7,388,572; 7,442,587; 7,492,497; 7,535,624; 7,551,346; 7,554,712; 7,583,427; 7,598,173; 7,605,799; 7,636,191; 7,649,674; 7,667,886; 7,672,040; 7,688,497; 7,733, U.S. Patent Nos. 335; 7,785,988; 7,843,626; 7,859,637; 7,893,435; 7,898,717; 7,957,053; 7,986,450; 8,009,344; 8,027,081; 8,049,947; 8,077,141; 8,089,453; 8,208,193; 8,373,211; 9,726,957; 10,520,786; 10,585,325; and 11,513,414; and U.S. Patent No. 2002 / 0060321;2004 / 0105036; 2005 / 0122306; 2005 / 0122563; 2007 / 0052757; 2007 / 0097489; 2007 / 0109219; 2007 / 0211002; 2009 / 0122389; 2009 / 0315044; 2010 / 0265239; 2011 / 0026101; 2011 / 014 U.S. Patent Application Publications Nos. 0744; 2011 / 0187683; 2011 / 0187689; 2011 / 0286082; 2011 / 0286086; 2011 / 0292319; 2011 / 0292493; 2011 / 0292494; 2011 / 0297309; 2011 / 0310459; and 2012 / 0182599; and International Application Publication No. WO 00 / 38000; European Patents Nos. 1,099,207 B1 and 1,145,072 B1;

[0017] (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;

[0018] (f) A method for driving a display; see, for example, U.S. Patents 7,012,600; 7,119,772; 7,453,445 and 10,475,396;

[0019] (g) Applications of displays; see, for example, U.S. Patents 7,312,784 and 8,009,348; and

[0020] (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.

[0021] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer dispersion electrophoretic display, wherein the electrophoretic medium comprises discrete droplets of a plurality of electrophoretic media and a continuous phase of polymeric material, and recognize that although the discrete capsules are not associated with each individual droplet, the discrete droplets of electrophoretic media within such a polymer dispersion electrophoretic display can also be considered as capsules or microcapsules; see, for example, U.S. Patent No. 6,866,760 mentioned above. Therefore, for the purposes of this application, such polymer dispersion electrophoretic media are considered a subtype of encapsulated electrophoretic media.

[0022] One related type of electrophoretic display is the so-called "microcell electrophoretic display." In a microcell electrophoretic display, charged particles and fluids are not encapsulated within microcapsules, but rather contained within multiple cavities formed within a carrier medium, typically a polymer film. See, for example, U.S. Patents 6,672,921 and 6,788,449, both of which have been assigned to Sipix Imaging, Inc.

[0023] Although electrophoretic media are typically opaque (because, for example, in many electrophoretic media, particles essentially block visible light transmission through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode," where one display state is substantially opaque and the other is translucent. See, for example, U.S. Patents 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectric electrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optic displays are also capable of operating in a shutter mode. Electrophoretic media operating in shutter mode can be used in multilayer structures for full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer further away from the viewing surface.

[0024] Encapsulated electrophoretic displays typically do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic displays and offer further advantages such as the ability to print or coat displays on a variety of flexible and rigid substrates (the term "printing" is used to include all forms of printing and coating, including but not limited to: volumetric coating, such as patch die coating, slot or extrusion coating, cascade coating, curtain coating; roll coating, such as doctor blade coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques). Therefore, the resulting display can be flexible. Furthermore, because the display medium can be printed (using various methods), the display itself can be manufactured at low cost.

[0025] Electro-optic displays typically include an electro-optic material layer and at least two other layers disposed on opposite sides of the electro-optic material layer, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both electrode layers are patterned to define pixels of the display. For example, one electrode layer may be patterned as an elongated row electrode, and the other electrode layer may be patterned as an elongated column electrode extending perpendicularly to the row electrode, with pixels defined by the intersection of the row and column electrodes. Alternatively and more commonly, one electrode layer has the form of a single continuous electrode, and the other electrode layer is patterned as a matrix of pixel electrodes, where each pixel electrode defines a pixel of the display. In another type of electro-optic display, intended for use with a stylus, printhead, or similar removable electrodes separate from the display, only one of the layers adjacent to the electro-optic material layer contains electrodes, and the layers on opposite sides of the electro-optic material layer are typically protective layers designed to prevent damage to the electro-optic material layer by the removable electrodes.

[0026] The fabrication of a three-layer electro-optic display typically involves at least one lamination operation. For example, several of the aforementioned MIT and E Ink patents and applications describe methods for fabricating encapsulated electrophoretic displays, wherein an encapsulated electrophoretic medium is coated onto a flexible substrate containing microcapsules in an adhesive, the flexible substrate containing an indium tin oxide (ITO) or similar conductive coating (which serves as an electrode in the final display) on a plastic film, and the microcapsule / adhesive coating is dried to form a coherent layer of electrophoretic medium firmly adhered to the substrate. A backplane is fabricated separately, comprising a pixel electrode array and a suitable conductor layout connecting the pixel electrodes to driving circuitry. To form the final display, a substrate with the capsule / adhesive layer on it is laminated to the backplane using a laminating adhesive (a very similar method can be used to fabricate an electrophoretic display usable with a stylus or similar movable electrode by replacing the backplane with a simple protective layer, such as a plastic film, on which the stylus or other movable electrode can slide). In a preferred form of this method, the backplane itself is flexible and is fabricated by printing pixel electrodes and conductors onto a plastic film or other flexible substrate. An obvious lamination technique for mass-producing displays using this process is roller lamination using laminating adhesives. Similar manufacturing techniques can be used for other types of electro-optic displays. For example, microcell electrophoretic media or rotating dual-color cell media can be laminated to the backplane in essentially the same manner as encapsulated electrophoretic media.

[0027] As discussed in U.S. Patent No. 6,982,178 (see column 3, lines 63 through 5, lines 46), many components used in solid-state electro-optic displays, as well as methods for manufacturing such displays, are derived from technologies used in liquid crystal displays (LCDs), which are also electro-optic displays, albeit using a liquid medium instead of a solid medium. For example, a solid-state electro-optic display may utilize an active matrix backplane comprising an array of transistors or diodes and corresponding pixel electrode arrays, and “continuous” front electrodes on a transparent substrate (in the sense of electrodes extending across multiple pixels and typically throughout the entire display). These components are essentially the same as those in LCDs. However, methods used to assemble LCDs cannot be used for solid-state electro-optic displays. LCDs are typically assembled by forming a backplane and front electrodes on separate glass substrates, then bonding these components together with small holes between them, placing the resulting assembly in a vacuum, and immersing the assembly in a liquid crystal bath, allowing liquid crystal to flow through the holes between the backplane and front electrodes. Finally, with the liquid crystal in place, the holes are sealed to provide the final display.

[0028] The LCD assembly process cannot be easily transferred to solid-state electro-optic displays. Because the electro-optic material layer is solid, it must exist between the backplate and the front electrode before they can be fixed together. Furthermore, unlike liquid crystal materials which are simply placed between the front electrode and the backplate without being bonded to either, the solid-state electro-optic material layer typically needs to be bonded to both. In most cases, the solid-state electro-optic material layer is formed on the front electrode, as this is generally easier than forming the dielectric on the backplate containing the circuitry. The front electrode / electro-optic material layer combination is then laminated onto the backplate, usually by covering the entire surface of the electro-optic material layer with adhesive and laminating under heat, pressure, and possibly vacuum. Therefore, most existing final lamination methods for solid-state electrophoretic displays are essentially batch processes, where the electro-optic material layer, laminating adhesive, and backplate are (typically) placed together immediately before final assembly, and a method better suited for mass production is needed.

[0029] The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling a solid-state electro-optic display (including an encapsulated electrophoretic display) that is well-suited for mass production. Essentially, the patent describes a so-called “front panel laminate” (“FPL”) comprising, in sequence: a light-transmitting conductive layer; an electro-optic material layer electrically in contact with said conductive layer; an adhesive layer; and a release sheet. Typically, the light-transmitting conductive layer is carried on a light-transmitting substrate, which is preferably flexible, meaning that the substrate can be manually wound around a roller with a diameter of (approximately) 10 inches (254 mm) without permanent deformation. The term “light-transmitting” in this patent and herein is used to mean that the layer, as defined herein, transmits sufficient light to allow an observer to view through the layer to observe changes in the display state of the electrophoretic medium, typically through the conductive layer and an adjacent substrate (if present); where the electrophoretic medium exhibits a change in reflectivity at non-visible wavelengths, the term “light-transmitting” should of course be interpreted as transmission at the relevant non-visible wavelengths. The substrate is typically a polymer film and usually has a thickness ranging from about 1 to about 25 mils (25 to 634 μm), preferably from about 2 to about 10 mils (51 to 254 μm). The conductive layer is preferably a thin metal or metal oxide layer, such as an aluminum or ITO layer, or it may be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, from EI du Pont de Nemours & Company in Wilmington, Delaware, under the name "aluminized Mylar" ("Mylar" is a registered trademark), and such commercial materials can be used in front panel laminates with good results.

[0030] Assembling an electro-optic display using such a front-panel laminate can be achieved by removing the release liner from the front-panel laminate and bringing the adhesive layer into contact with the backplate while effectively adhering the adhesive layer to the backplate, thereby fixing the adhesive layer, electrophoretic dielectric layer, and conductive layer to the backplate. This process is well-suited for mass production because the front-panel laminate can be mass-produced, typically using roll-to-roll coating technology, and then cut into sheets of any size required for use with a specific backplate.

[0031] U.S. Patent No. 7,561,324 describes a so-called "dual release sheet," which is essentially a simplified version of the front panel laminate of the aforementioned U.S. Patent No. 6,982,178. One form of the dual release sheet includes a layer of solid electro-optic material sandwiched between two adhesive layers, wherein one or both adhesive layers are covered by the release sheet. Another form of the dual release sheet includes a layer of solid electro-optic material sandwiched between two release sheets. Both forms of dual release sheets are intended for use in processes generally similar to those used for assembling electro-optic displays from the already described front panel laminate, but involving two separate laminations; typically, in the first lamination, the dual release sheet is laminated to the front electrode to form a front sub-assembly, and then in the second lamination, the front sub-assembly is laminated to the back panel to form the final display, although the order of these two laminations can be reversed if desired.

[0032] U.S. Patent No. 7,839,564 describes a so-called "inverted front panel laminate," a variation of the front panel laminate described in U.S. Patent No. 6,982,178. This inverted front panel laminate sequentially includes at least one of a light-transmitting protective layer and a light-transmitting conductive layer; an adhesive layer; a solid electro-optic material layer; and a release liner. This inverted front panel laminate is used to form an electro-optic display having a laminated adhesive layer between the electro-optic material layer and the front electrode or front substrate; a second, generally thin, adhesive layer may or may not be present between the electro-optic material layer and the backplate. Such an electro-optic display can combine good resolution with good low-temperature performance.

[0033] In high-resolution displays, each individual pixel must be addressable without interference from addressing adjacent pixels (regardless of whether the electrophoretic medium used is bistable). One way to achieve this is to provide an array of nonlinear elements, such as an array of transistors or diodes, where at least one nonlinear element is associated with each pixel to produce an active matrix display, as mentioned above. Addressing (pixel) electrodes are connected to a suitable voltage source via their associated nonlinear elements, and these addressing (pixel) electrodes address a pixel. By convention, in high-resolution arrays, pixels are arranged in a two-dimensional array of rows and columns such that any particular pixel is uniquely defined by the intersection of a designated row and a designated 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 source-to-row and gate-to-column assignments are conventional and can be reversed if desired. Row electrodes are connected to row drivers, which essentially ensure that only one row is selected at any given time—that is, a voltage is applied to the selected row electrode to ensure that all transistors in the selected row are conductive, while a voltage is applied to all other rows to ensure that all transistors in these unselected rows remain non-conductive. Column electrodes are connected to column drivers, which apply selected voltages to each column electrode to drive the pixels in the selected row to their desired optical state. The aforementioned voltages are relative to a common front electrode, which is typically positioned on the side of the electrophoretic medium opposite the nonlinear array and extends across the entire display. After a preselected interval known as the “line addressing time,” the selected row is deselected, the next row is selected, and the voltage on the column drivers changes, causing the next row of the display to be written. This process is repeated, resulting in line-by-line writing across the entire display.

[0034] In the following discussion, the term "waveform" will be used to refer to a curve of voltage change over time that influences the transition of a pixel from a specific initial gray level to a specific final gray level. Typically, such a waveform contains multiple waveform elements; where these elements are inherently rectangular (i.e., where a given element contains an application of a constant voltage for a given period of time); these elements may be referred to as "pulses" or "drive pulses." The term "drive scheme" refers to a set of waveforms sufficient to influence the possible transitions between all gray levels of a particular display. A display may use multiple drive schemes; for example, U.S. Patent No. 7,012,600 teaches that a drive scheme may need to be modified based on parameters such as the display's temperature or the time it has been operating during its lifespan. Therefore, a display may be equipped with multiple different drive schemes for use under conditions such as different temperatures. A set of drive schemes used in this way may be referred to as a "set of related drive schemes."

[0035] Electro-optic displays comprising electrophoretic media containing black and white particles are well known in the art and have been used in e-readers, electronic notebooks, and other devices for over a decade. Typically, the black and white particles contain inorganic pigments. More recently, electro-optic displays comprising electrophoretic media containing colored particles, such as yellow, red, and other colored particles, have been introduced to the market. Typically, such electro-optic displays contain colored particles containing organic pigments in addition to white particles and optionally black particles. For color displays, organic pigments are superior to inorganic pigments because they provide more vibrant colors and significantly higher chromaticity. However, in the presence of ultraviolet and visible light, organic pigments generally exhibit lower long-term color stability than inorganic pigments. Therefore, there is a need to develop color electro-optic displays comprising electrophoretic media containing organic pigments, wherein the color quality of the electro-optic display image remains stable even after prolonged display use. The inventors of this invention have surprisingly discovered that color electro-optic devices comprising electrophoretic media containing organic pigments and electron acceptor molecules significantly improve the long-term color quality of electro-optic display images. Invention Overview

[0036] Therefore, the present invention provides a color electro-optic display, which sequentially comprises a first electrode layer, an electro-optic material layer, and a second electrode layer. The first electrode layer includes a light-transmitting electrode. The second electrode layer includes a plurality of pixel electrodes. The electro-optic material layer includes an electrophoretic medium encapsulated in a plurality of microunits or microcapsules. The electrophoretic medium includes a plurality of first-type charged pigment particles, a plurality of second-type charged pigment particles, a lightfastness additive, and a nonpolar liquid. At least one of the first-type and second-type charged pigment particles comprises an organic pigment. The lightfastness additive is present in the electrophoretic medium at a content of 0.1% to 6.0% by weight.

[0037] The electro-optic material layer may include multiple microcapsules and an adhesive, each microcapsule containing an electrophoretic medium. The color electro-optic display containing the electrophoretic medium encapsulated in multiple microcapsules may further include a first adhesive layer disposed between the electro-optic material layer and the second electrode layer. In addition to the first adhesive layer, the color electro-optic display containing the electrophoretic medium encapsulated in multiple microcapsules may further include a second adhesive layer disposed between the electro-optic material layer and the first electrode layer.

[0038] The electro-optic material layer may include a plurality of micro-units. Each of the plurality of micro-units may have a micro-unit bottom, a partition wall, an opening, and a sealing layer spanning the opening. The sealing layer may be adjacent to the second electrode layer. Each micro-unit is filled with an electrophoretic dielectric. The color electro-optic display having a plurality of micro-units in the electro-optic material layer may further include an adhesive layer disposed between the sealing layer and the second electrode layer.

[0039] In addition to the plurality of charged pigment particles of the first and second types, the electrophoretic medium of the color electro-optic display of the present invention may also contain a plurality of charged pigment particles of the third type. The pigment particles of the first, second, and third types may have different colors selected from white, black, cyan, magenta, yellow, blue, green, and red. The pigment particles of the first, second, and third types may be (a) white, (b) black, and (c) yellow or red, respectively.

[0040] In addition to the plurality of charged pigment particles of the first, second, and third types, the electrophoretic medium of the color electro-optic display of the present invention may also contain a plurality of charged pigment particles of the fourth type. The pigment particles of the first, second, third, and fourth types may have different colors selected from white, black, cyan, magenta, yellow, blue, green, and red. The pigment particles of the first, second, third, and fourth types may be white, cyan, magenta, and yellow, respectively. The pigment particles of the first, second, third, and fourth types may be white, blue, red, and green, respectively.

[0041] In addition to the plurality of charged pigment particles of the first, second, third, and fourth types, the electrophoretic medium of the color electro-optic display of the present invention may also include a plurality of charged pigment particles of the fifth type. The charged pigment particles of the first, second, third, fourth, and fifth types may have different colors selected from white, black, cyan, magenta, yellow, blue, green, and red. The pigment particles of the first, second, third, fourth, and fifth types may be white, black, red, blue, and green, respectively.

[0042] The lightfastness additive for the electrophoretic medium of a color electro-optic display of the present invention improves the lightfastness of the display. The lightfastness additive is an electron acceptor. The lightfastness additive may be selected from substituted 1,2-benzoquinone, substituted 1,4-benzoquinone, substituted naphthoquinone, and substituted anthraquinone. The substituted 1,2-benzoquinone, substituted 1,4-benzoquinone, substituted naphthoquinone, and substituted anthraquinone may have at least one substituent comprising an alkyl, cycloalkyl, or alkenyl group. The at least one substituent may have 10 or more carbon atoms. The at least one substituent may have 10 to 120 carbon atoms.

[0043] The substituted 1,2-benzoquinone, substituted 1,4-benzoquinone, substituted naphthoquinone, and substituted anthraquinone may have at least one substituent, which is represented by Formula I or Formula II, wherein n is an integer from 2 to 20, and m is an integer from 1 to 20.

[0044] .

[0045] The lightfastness additive in the electrophoretic medium may be a substituted 1,4-benzoquinone, which is represented by Formula III.

[0046]

[0047] R1 can be represented by formula I or formula II, where n can be an integer from 2 to 20, and m can be an integer from 1 to 20, or from 2 to 13. R2 to R4 can be independently selected from hydrogen, alkyl groups, alkenyl groups, aryl groups, and heteroatom groups containing heteroatoms of groups V-VII of the periodic table.

[0048] The lightfastness additive of the electrophoretic medium can be represented by Formula III, wherein R1 can be represented by Formula II, m is an integer from 2 to 20, and each of R2, R3 and R4 is independently selected from hydrogen, alkyl, alkenyl and alkoxy groups.

[0049] The lightfastness additive of the electrophoretic medium can be represented by Formula III, wherein R1 can be represented by Formula II, m is an integer from 2 to 20, wherein R2 can be methyl, and wherein R3 and R4 can be methoxy groups.

[0050] The lightfastness additive of the electrophoretic medium can be represented by Formula III, wherein R1 can be represented by Formula II, m is an integer from 2 to 20, R2 can be hydrogen, and R3 and R4 can be methyl groups.

[0051] The lightfastness additive may be a substituted 1,4-benzoquinone represented by Formula IV.

[0052] .

[0053] The lightfastness additive may be a substituted 1,4-benzoquinone (ubiquinone-10) represented by formula V.

[0054] .

[0055] The lightfastness additive in the electrophoretic medium may be a substituted 1,4-benzoquinone, represented by formula VI. Each of R5, R6, and R7 may be independently selected from hydrogen, alkyl, alkenyl, and alkoxy groups. In formula VI, o is an integer from 2 to 20.

[0056] .

[0057] The lightfastness additive for the electrophoretic medium can be a substituted naphthoquinone, represented by formula VII. R8, R9, R 10 R 11 and R 12 Each of the groups is independently selected from hydrogen, alkyl, alkenyl, and alkoxy groups. In Formula VII, p is an integer from 2 to 20.

[0058] .

[0059] The lightfastness additive in the electrophoretic medium can be a substituted naphthoquinone, represented by formula VIII. 13 R 14 R 15 R 16 and R 17 Each of the groups can be independently selected from hydrogen, alkyl, alkenyl, and alkoxy groups. In Formula VIII, q is an integer from 2 to 20. The integer p in Formula VIII can be selected from 3, 4, 7, and 9.

[0060] In the example of the lightfastness additive represented by Formula VIII, R 13 R 14 R 15 R 16 and R 17 It can be hydrogen, and R 21 It is a methyl group. The integer q in the example can be 3, 4, 7, or 9.

[0061] . Brief description of the attached diagram

[0062] Figure 1 This is a side view of a color electro-optic display containing an electrophoretic medium encapsulated in microcapsules. The color electrophoretic display sequentially comprises: a first electrode layer, an electro-optic material layer, a first adhesive layer, and a second electrode layer.

[0063] Figure 2 This is a side view of a color electro-optic display containing an electrophoretic medium encapsulated in microcapsules. The color electrophoretic display sequentially comprises: a first electrode layer, a second adhesive layer, an electro-optic material layer, and the second electrode layer.

[0064] Figure 3 This is a side view of a color electro-optic display containing an electrophoretic medium encapsulated in microcells. The color electrophoretic display sequentially includes: a first electrode layer, an electro-optic material layer containing a sealing layer, a first adhesive layer, and a second electrode layer.

[0065] Figure 4 , 5Images 6 are micrographs of microcapsules of electro-optic material layers used for three different electrophoretic media. Invention Details

[0066] As used herein, the term "electron acceptor" or its synonym "electron acceptor molecule" refers to a compound that accepts electrons from another molecule, which is the electron donor. That is, an electron acceptor can be an oxidizing agent.

[0067] The terms “substituted 1,2-benzoquinone”, “substituted 1,4-benzoquinone”, “substituted naphthoquinone” and “substituted anthraquinone” are molecules whose molecular structure includes 1,2-benzoquinone, 1,4-benzoquinone, naphthoquinone and anthraquinone ring structures and at least one substituent directly attached to the 1,2-benzoquinone, 1,4-benzoquinone, naphthoquinone and anthraquinone ring structures.

[0068] As used herein, the term "alkyl" refers to a hydrocarbon group that can be linear or branched. The hydrocarbon group contains a carbon-carbon single bond. The hydrocarbon group does not contain a carbon-carbon double bond or a carbon-carbon triple bond.

[0069] As used herein, the term "cycloalkyl" refers to a saturated hydrocarbon containing a ring structure. The saturated hydrocarbon may comprise monocyclic, bicyclic, tricyclic, or other polycyclic hydrocarbon groups. The carbon atoms in the ring structure may contain substituents, which may be linear or branched.

[0070] As used herein, the term "alkenyl" refers to a hydrocarbon group having at least one carbon-carbon double bond. The hydrocarbon group may be linear or branched.

[0071] As used in this article, the term "aryl" refers to a hydrocarbon group that contains an aromatic ring.

[0072] As used herein, the term "heteroatomic group" refers to an alkyl, cycloalkyl, alkenyl, or aryl group that contains at least one heteroatom from Groups V-VII of the periodic table in addition to carbon and hydrogen atoms.

[0073] As used herein, the term "aliphatic hydrocarbons" includes saturated and unsaturated, non-aromatic, linear (i.e., straight-chain), branched, acyclic, and cyclic hydrocarbons.

[0074] A compound is considered "soluble" in a liquid if at least 1 gram of the compound can dissolve in 100 grams of the liquid.

[0075] The term "lightfastness" in the context of color electro-optic displays relates to the consistency of color quality of an image over time. As the color quality of an image deteriorates over time, it means that the total color gamut that the color electro-optic display can provide decreases.

[0076] A typical color 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 A side view showing a basic structural example of a portion of a color electro-optic display with microcapsules. The color electro-optic display 100 includes a first electrode layer 101 containing light-transmitting electrodes, an electro-optic material layer 102, a first adhesive layer 104, and a second electrode layer 103, the second electrode layer containing a plurality of pixel electrodes. The first adhesive layer 104 connects the electro-optic material layer 102 to the second electrode layer. The electro-optic material layer 102 contains a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and contains an electrophoretic medium 122 having charged pigment particles in a non-polar liquid. The electrophoretic medium 122 contains a plurality of first-type charged pigment particles and a plurality of second-type pigment particles. At least one of the first and second-type charged pigment particles contains an organic pigment. The electrophoretic medium may also contain a plurality of third-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fourth-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fifth-type charged pigment particles. The electrophoretic medium 122 also contains a lightfastness additive. Typically, multiple microcapsules are contained within a polymer binder 132. A viewer can view the image on the display 100 from the viewing side 150. At least one type of charged pigment may comprise an organic pigment. The colored electro-optic material layer 100 may be constructed from a front-panel laminate as described in the background of this invention.

[0077] Another example of a color electro-optical display is shown in Figure 2 . Figure 2A side view showing a basic structural example of a portion of a color electro-optic display with microcapsules. The electro-optic display 200 has a viewing side 150. It sequentially includes: a first electrode layer 101 containing light-transmitting electrodes, a second adhesive layer 105, an electro-optic material layer 102, a first adhesive layer 104, and a second electrode layer 103 containing a plurality of pixel electrodes. The second adhesive layer 105 connects the first electrode layer 101 to the electro-optic material layer 102. The first adhesive layer 104 connects the electro-optic material layer 102 to the second electrode layer. The electro-optic material layer 102 contains a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and contains an electrophoretic medium 122 having charged pigment particles in a non-polar liquid. The electrophoretic medium 122 contains a plurality of first-type charged pigment particles and a plurality of second-type charged pigment particles. At least one of the first and second-type charged pigment particles contains an organic pigment. The electrophoretic medium may also contain a plurality of third-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fourth-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fifth-type charged pigment particles. The electrophoretic medium 122 also contains lightfastness additives. Typically, multiple microcapsules are contained within a polymer binder 132. The colored electro-optic material layer 100 may be constructed from a dual release sheet as described in the background of this invention.

[0078] Figure 1 and Figure 2 The microencapsulated color electro-optic display may also include a light-transmitting front substrate ( Figure 1 and Figure 2 (Not shown in the image), the front substrate is adjacent to the first electrode layer 101, wherein the electrode layer is disposed between the front substrate and the electro-optic material layer (for Figure 1 (for the display) or disposed between the front substrate and the second adhesive layer (for Figure 1 The front substrate can be a plastic film, such as a polyethylene terephthalate (PET) sheet with a thickness of 25 to 200 µm. The front substrate may also include one or more additional layers, such as a protective layer that absorbs ultraviolet radiation, a barrier layer that prevents oxygen or moisture from entering the display, and an anti-reflective coating that improves the optical properties of the display.

[0079] Examples of color electro-optic displays containing micro-units are shown in Figure 3 As shown in the image. Figure 3The color electro-optic display 300 sequentially includes: a first electrode layer 201, an electro-optic material layer 202, an adhesive layer 204, and a second electrode layer 203 comprising a plurality of pixel electrodes. The adhesive layer 204 connects the sealing layer 232 of the electro-optic material layer 202 to the second electrode layer 203. The electro-optic material layer 202 of the color electro-optic display 300 comprises a plurality of microcells 212 and a sealing layer 232. Each of the plurality of microcells 212 has a bottom 242, a partition wall 252, and an opening, and the sealing layer 232 spans the opening of each microcell. Each of the plurality of microcells 212 comprises an electrophoretic medium 222. The electrophoretic medium 222 comprises a plurality of first-type charged pigment particles 272 and a plurality of second-type charged pigment particles 262 in a non-polar liquid. At least one of the first-type and second-type charged pigment particles (272 and 262) comprises an organic pigment. The electrophoretic medium 222 may also comprise a plurality of third-type charged pigment particles. The electrophoretic medium 222 may also contain multiple charged pigment particles of type IV. The electrophoretic medium 222 may also contain multiple charged pigment particles of type V. The electrophoretic medium 222 also contains lightfastness additives. A viewer can view the image on the display 100 from the viewing side 250.

[0080] Figure 3 Micro-unit color electro-optic displays may also include a light-transmitting front substrate ( Figure 3 (Not shown in the image), the front substrate is adjacent to the first electrode layer 201, wherein the electrode layer is disposed between the front substrate and the electro-optic material layer. The front substrate may be a plastic film, such as a polyethylene terephthalate (PET) sheet having a thickness of 25 to 200 µm. The front substrate may also 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.

[0081] exist Figure 1 , 2 In the electro-optical display of 3, the first electrode layer may be a conductive layer having a thin, continuous coating of conductive material with minimal inherent absorption of electromagnetic radiation in the visible spectrum, such as indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), graphene, or the like.

[0082] Microcells can be formed via batch processes or continuous roll-to-roll processes as disclosed in U.S. Patent No. 6,933,098. The latter provides a continuous, low-cost, high-throughput manufacturing technique for producing compartments for a variety of applications, including electro-optical display devices. Microcell arrays suitable for use in this invention can be manufactured using micro-embossing.

[0083] The electrophoretic medium of the color electro-optic display of the present invention comprises charged pigment particles, a lightfastness additive, and a nonpolar liquid. The nonpolar liquid may include aliphatic hydrocarbons. The lightfastness additive is an electron acceptor. The lightfastness additive is present in the electrophoretic medium at a content of 0.1 to 6.0% by weight, based on the weight of the electrophoretic medium. Alternatively, the lightfastness additive may be present in the electrophoretic medium at a content of 0.2 to 5.0%, 0.4 to 4.0%, 0.5 to 3.0%, 0.6 to 2.0%, or 0.7 to 1.5% by weight, based on the weight of the electrophoretic medium. The lightfastness additive is soluble in the nonpolar liquid of the electrophoretic medium.

[0084] The lightfastness additive may be selected from substituted 1,2-benzoquinone, substituted 1,4-benzoquinone, substituted naphthoquinone, and substituted anthraquinone. The substituted 1,2-benzoquinone, substituted 1,4-benzoquinone, substituted naphthoquinone, and substituted anthraquinone may have at least one substituent comprising an alkyl, cycloalkyl, or alkenyl group. The at least one substituent may have 8 or more carbon atoms, 10 or more carbon atoms, 12 or more carbon atoms, 15 or more carbon atoms, 20 or more carbon atoms, 25 or more carbon atoms, 30 or more carbon atoms, 35 or more carbon atoms, 40 or more carbon atoms, 60 or more carbon atoms, 80 or more carbon atoms, 100 or more carbon atoms, or 110 or more carbon atoms.

[0085] The at least one substituent may have 8 to 120 carbon atoms, 10 to 120 carbon atoms, 12 to 110 carbon atoms, 15 to 110 carbon atoms, 20 to 110 carbon atoms, 25 to 110 carbon atoms, 30 to 110 carbon atoms, or 40 to 110 carbon atoms. The at least one substituent may have 8 to 105 carbon atoms, 10 to 100 carbon atoms, 12 to 90 carbon atoms, 15 to 90 carbon atoms, 20 to 85 carbon atoms, 25 to 80 carbon atoms, 30 to 85 carbon atoms, or 40 to 85 carbon atoms.

[0086] The lightfastness additive may be a substituted 1,2-benzoquinone, a substituted 1,4-benzoquinone, a substituted naphthoquinone, or a substituted anthraquinone having at least one substituent, wherein the at least one substituent is represented by Formula I or Formula II, wherein n is an integer from 2 to 20, and wherein m is an integer from 1 to 20.

[0087] .

[0088] The lightfastness additive may be a substituted 1,4-benzoquinone, represented by Formula III, wherein R1 is represented by Formula I or Formula II, where n is an integer from 2 to 20, and m is an integer from 1 to 20. The integer n may be 1 to 20, 2 to 18, 2 to 15, 3 to 12, or 3 to 10. The integer m may be 1 to 20, 1 to 18, 2 to 18, 2 to 15, 3 to 15, 3 to 12, 3 to 10, or 4 to 10. The substituent R1 may also be an alkyl group containing 10 to 100 carbon atoms, 10 to 80 carbon atoms, 10 to 70 carbon atoms, 10 to 50 carbon atoms, 10 to 30 carbon atoms, 10 to 20 carbon atoms, or 10 to 15 carbon atoms. Substituents R2 to R4 may be independently selected from hydrogen, alkyl groups, alkenyl groups, aryl groups, and heteroatom groups containing heteroatoms from groups V-VII of the periodic table. The heteroatoms may be selected from nitrogen, oxygen, halogen, phosphorus, or sulfur.

[0089]

[0090] The lightfastness additive can be 1,4-benzoquinone represented by Formula III, where the substituent R1 is represented by Formula II, the integer m is 2 to 20, and each of R2, R3, and R4 is independently selected from hydrogen, alkyl, alkenyl, and alkoxy groups. The lightfastness additive can be 1,4-benzoquinone represented by Formula III, where the substituent R1 is represented by Formula II, the integer m is 2 to 20, R2 is hydrogen, and R3 and R4 are methyl groups.

[0091] The lightfastness additive can be 1,4-benzoquinone represented by Formula III, where substituent R1 is represented by Formula II, m is 9, R2 is hydrogen, and R3 and R4 are methyl groups. The molecular structure of the lightfastness additive is represented by Formula IV.

[0092] .

[0093] The lightfastness additive can be 1,4-benzoquinone represented by Formula III, where substituent R1 is represented by Formula II, m is 10, R2 is a methyl group, and R3 and R4 are methoxy groups. The molecular structure of the lightfastness additive is represented by Formula V. Formula V is referred to as ubiquinone-10 in the literature.

[0094] .

[0095] The lightfastness additive can be 1,4-benzoquinone represented by Formula III, where substituent R1 can be represented by Formula II, m is 2, R2 is a methyl group, and R3 and R4 are methoxy groups.

[0096] The lightfastness additive may be 1,4-benzoquinone represented by formula VI, wherein each of R5, R6 and R7 may be independently selected from hydrogen, alkyl, alkenyl and alkoxy groups, and wherein o is an integer from 2 to 20.

[0097] .

[0098] The lightfastness additive can be a substituted naphthoquinone represented by formula VII, wherein R8, R9, R... 10 R 11 and R 12 Each of them can be independently selected from hydrogen, alkyl, alkenyl and alkoxy groups, and p is an integer from 2 to 20.

[0099] .

[0100] The lightfastness additive may be a substituted naphthoquinone represented by formula VIII, wherein R 13 R 14 R 15 R 16 and R 17 Each of them can be independently selected from hydrogen, alkyl, alkenyl and alkoxy groups, and q is an integer from 2 to 20.

[0101] .

[0102] The lightfastness additive may be a substituted naphthoquinone represented by formula VIII, where q is an integer from 2 to 20, and R 13 R 14 R 15 R 16 It is hydrogen, and R 17 It is a methyl group. The integer q can be selected from 3, 4, 7, and 9.

[0103] The electrophoretic medium of the innovative color electro-optic display of the present invention comprises two or more types of charged pigment particles. The electrophoretic medium of the innovative color electro-optic display of the present invention comprises a plurality of first-type charged pigment particles and a plurality of second-type charged pigment particles. The first-type charged pigment particles have a different color than the second-type charged pigment particles. At least one of the first and second charged pigment particles comprises an organic pigment. The electrophoretic medium of the color electro-optic display of the present invention may further comprise a plurality of third-type charged pigment particles, which may have a different color than the first and second charged pigment particles. The third charged pigment particles may comprise organic pigments. The electrophoretic medium of the color electro-optic display of the present invention may further comprise a plurality of fourth-type charged pigment particles, which may have a different color than the first, second, and third charged pigment particles. The third charged pigment particles may comprise organic pigments. The electrophoretic medium of the color electro-optic display of the present invention may further comprise a plurality of fifth-type charged pigment particles, which may have a different color than the first, second, third, and fourth charged pigment particles. The fifth charged pigment particles may comprise organic pigments.

[0104] Each type of charged pigment particle in the electrophoretic medium can carry either a positive or negative charge. If the electrophoretic medium contains two types of charged pigment particles, namely first and second types, the first type of charged pigment particles can carry a negative charge (or a positive charge), and the second type of charged pigment particles can carry a positive charge (or a negative charge). When an electric field is applied across the electro-optic material layer through the pixel electrode via the transparent conductive layer and the backplate, the first type of charged pigment particles in the electrophoretic medium move towards the positive electrode, and the second type of charged pigment particles move towards the negative electrode. This results in an observer viewing the display from the viewing side seeing either the first type of charged pigment particles or the second type of charged pigment particles corresponding to the pixel electrode, depending on whether the transparent conductive layer is positively or negatively charged relative to the pixel electrode.

[0105] In one example, the electrophoretic medium contains three types of charged pigment particles, each with a different color from the others. Two of the three types of charged pigment particles may carry a positive charge, and one type of charged pigment particle carries a negative charge. At least one of the types of charged pigment particles contains an organic pigment. Two of the types of charged pigment particles may contain organic pigments. The colors of the three types of charged pigment particles can be selected from white, black, yellow, red, blue, cyan, and magenta.

[0106] In another example, the electrophoretic medium contains four types of charged pigment particles. Each type of charged pigment particle may have a different color. Two of the charged pigment particles of said type may carry a positive charge, and two of said type may carry a negative charge. Alternatively, three of said type of charged pigment particles may carry a positive charge, and one type of charged pigment particle may carry a negative charge. At least one of said type of charged pigment particles contains an organic pigment. Two types of charged pigment particles may contain organic pigments. The colors of the four types of charged pigment particles may be selected from white, black, yellow, red, blue, cyan, and magenta. For example, the electrophoretic particles may contain white, cyan, magenta, and yellow. Cyan, magenta, and yellow charged particles may carry a positive charge, and white charged particles may carry a negative charge.

[0107] In another example, the electrophoretic medium contains five types of charged pigment particles. Each type of charged pigment particle may have a different color. Three of the charged pigment particles of said type may carry a positive charge, and two of said type may carry a negative charge. Alternatively, four of said type of charged pigment particles may carry a positive charge, and one type of charged pigment particle may carry a negative charge. At least one of said type of charged pigment particles contains an organic pigment. Two, three, or four types of charged pigment particles may contain organic pigments. The colors of the five types of charged pigment particles may be selected from white, black, green, yellow, red, blue, cyan, green, and magenta. For example, the electrophoretic particles may contain white, cyan, magenta, and yellow. Cyan, magenta, and yellow charged pigment particles may carry a positive charge, and white charged particles may carry a negative charge.

[0108] As mentioned above, organic pigments generally have lower long-term color stability than inorganic pigments. However, in terms of color, organic pigments are far more desirable because they exhibit much brighter and more saturated colors than inorganic pigments. That is, the color of organic pigments is less stable over time when exposed to ultraviolet or visible light. The lightfastness additives in the color electrophoretic medium of the color electro-optic display of the present invention significantly improve the lightfastness of the electro-optic display of the present invention.

[0109] While the mechanism by which the color quality of images in color electro-optic displays degrades during prolonged exposure to light is not fully understood, the inventors of this invention have observed that the addition of electron donor molecules, such as amines, to the electrophoretic media composition reduces the lightfastness of the color electro-optic display. Uncontrolled trace amounts of electron donor molecules are likely to be present in the materials used to prepare the electrophoretic composition. For example, charge control agents (CCAs) are surfactant-type molecules, typically quaternary ammonium salts, prepared by reacting an amine with a suitable alkylating agent. Incomplete alkylation results in the presence of some free amine, which, as mentioned above, is an electron donor. Because alkylating agents are toxic compounds, manufacturers of quaternary ammonium salts typically slightly reduce their addition for safety reasons. As a result, many commercially available or custom-made CCA molecules contain small amounts of free amine.

[0110] An example of an electron donor is ubiquinone-10, which is the completely reduced form of ubiquinone-10 (Formula V as shown above). The inventors of this invention have found that the addition of ubiquinone-10 (an electron donor molecule) to the electrophoretic medium of a color electro-optic display has a detrimental effect on the lightfastness of the display. Conversely, the inventors of this invention have found that electron acceptor molecules, such as ubiquinone-10, have a beneficial effect on the lightfastness of the color electro-optic display. An example of an electron acceptor evaluated for lightfastness additives is ubiquinone-10 (also known as coenzyme Q10). This material is an readily available, lipid-soluble electron acceptor. Other quinone molecules that are electron acceptors and are lipid-soluble (or soluble in the micelle core) are expected to exhibit similar behavior. Electrons can be photoexcited by absorbing light, without being limited to any particular theory. To prevent the excited electrons from negatively affecting the lightfastness of electro-optic displays, adding electron acceptors to the electrophoretic medium may mitigate the adverse effects of potential electron donors, since electron transfer occurs from electron donors or photoexcited pigment molecules to electron acceptors, rather than from electron donors or photoexcited pigment molecules to pigment molecules. Example

[0111] I. Preparation of pigment particles and dispersions in Isopar E

[0112] Example 1A The white pigment particles were prepared using titanium dioxide pigment cores comprising a polymer coating, as described in Example 1 of U.S. Patent No. 8,582,196. The polymer coating comprised lauryl methacrylate (LMA) and 2,2,2-trifluoroethyl methacrylate (TFEM) in a ratio of approximately 99:1. After polymerization, the solvent was replaced from toluene with Isopar E by repeated washing and removal of the supernatant.

[0113] Example 1BThe white pigment particles are prepared using titanium dioxide pigment cores, which include a polymer coating. The polymer coating is formed by the polymerization of lauryl methacrylate (LMA), 2,2,2-trifluoroethyl methacrylate (TFEM), and polysiloxane macromonomer (PDMS). After the polymerization reaction, the solvent is replaced from toluene with Isopar E by repeated washing and removal of the supernatant.

[0114] Example 2A The yellow pigment particles were prepared using CI Pigment Yellow 155 cores, which included a polymer coating. This polymer coating was formed by the polymerization of methyl methacrylate (MMA), 2,2,2-trifluoroethyl methacrylate (TFEM), and polysiloxane macromonomer (PDMS). After polymerization, the solvent was replaced from toluene with Isopar E by repeated washing and removal of the supernatant.

[0115] Example 2B: As summarized in Example 2A of U.S. Patent No. 9,697,778, a dispersion was prepared by grinding commercially available Pigment Yellow 155 particles using Solsperse 19,000 in Isopar E as a medium.

[0116] Example 3A The magenta pigment particles were prepared using magenta dimethylquinacridone pigment (CI Pigment Red 122), which included a polymer coating. The polymer coating was formed using vinyl benzyl chloride (VBC) and lauryl methacrylate (LMA), as described in Example 1 of U.S. Patent No. 9,697,778. After polymerization, the solvent was replaced from toluene with Isopar E by repeated washing and removal of the supernatant.

[0117] Example 4A The cyan pigment particles are prepared using cyan copper phthalocyanine pigment (CI Pigment Blue 15:3), which includes a polymer coating. The polymer coating is formed using methyl methacrylate monomer (MMA) and polysiloxane macromonomer (PDMS), as described in Example 7 of U.S. Patent No. 10,509,293.

[0118] II. Preparation of electrophoretic media.

[0119] Example 5AThe dispersion containing white pigment from Example 1A was combined with the dispersion containing yellow pigment from Example 2A, the dispersion containing magenta pigment from Example 3A, the dispersion containing cyan pigment from Example 4A, the charge control agent CCA-111, ubiquinone-10, Isopar E, and polyisobutylene (number average molecular weight 850,000). The structure and preparation of CCA-111 are described in U.S. Patent Application Publication No. 2020 / 0355978. The content of ubiquinone-10 in the electrophoresis medium of Example 5 was 3.0 wt% based on the weight of the electrophoresis medium.

[0120] Comparative Example 6A Comparative Example 6A was prepared similarly to Example 5A, but without any lightfastness additive, ubiquinone-10. It serves as a control electrophoresis medium. The conductivity of this electrophoresis medium was measured to be 430 pS / cm.

[0121] Example 7A The dispersion containing white pigment from Example 1B was combined with the dispersion containing yellow pigment from Example 2B, the dispersion containing magenta pigment from Example 3A, the dispersion containing cyan pigment from Example 4A, Solsperse 19,000, ubiquinone-10, Isopar E, and polyisobutylene (number average molecular weight 850,000). The content of ubiquinone-10 in the electrophoresis medium of Example 5 was 3.0% by weight, based on the weight of the electrophoresis medium. The conductivity of the electrophoresis medium was 417 pS / cm.

[0122] Comparative Example 8A A dispersion similar to the electrophoretic medium of Example 7A was prepared, except that ubiquinone-10 was used instead of ubiquinol-10. Ubiquinol-10 is the reduced form of ubiquinone-10. Ubiquinol-10 is not an electron acceptor but an electron donor. The conductivity of the electrophoretic medium was 449 pS / cm.

[0123]

[0124] Comparative Example 9A Prepare an electrophoresis medium similar to that of Example 7A and Comparative Example 8A, wherein the electrophoresis medium does not contain ubiquinone-10 or ubiquinol-10. That is, Comparative Example 9A is a control electrophoresis medium.

[0125] III. Encapsulation of electrophoretic media.

[0126] Example 5BThe electrophoretic medium from Example 5A was encapsulated in gelatin / gum arabic aggregates using the following method: Gelatin was dissolved in deionized water at 40°C and vigorously stirred. The electrophoretic medium from Example 1 was added dropwise to the stirred gelatin solution through a tube, the outlet of which was below the surface of the stirred solution. The resulting mixture was maintained at 42.5°C and continuously vigorously stirred to generate electrophoretic medium droplets in a continuous gelatin-containing aqueous phase. Then, an aqueous solution of gum arabic at 42.5°C was added to the mixture, and the pH of the mixture was lowered to approximately 5 to allow the gelatin / gum arabic aggregates to form, thereby forming microcapsules. The temperature of the resulting mixture was then lowered to 9°C, and an aqueous solution of glutaraldehyde (a crosslinking agent) was added. The resulting mixture was then heated to 25°C and vigorously stirred for 12 hours. The resulting microcapsules were separated by sieving using sieves with mesh sizes of 20 μm and 45 μm to obtain microcapsules with an average diameter of approximately 44 μm.

[0127] Comparative Example 6B The encapsulation process described in Example 5B was repeated for the encapsulation of the electrophoretic medium prepared in Comparative Example 6A.

[0128] Comparative Example 7B The encapsulation process described in Example 5B was repeated for the encapsulation of the electrophoretic medium prepared in Comparative Example 7A.

[0129] Comparative Example 8B The encapsulation process described in Example 5B was repeated for the encapsulation of the electrophoretic medium prepared in Comparative Example 8A.

[0130] Comparative Example 9B The encapsulation process described in Example 5B was repeated for the encapsulation of the electrophoretic medium prepared in Comparative Example 9A.

[0131] Samples of microcapsules from Examples 7B, 8B, and 9B were observed using a microscope. Microscopic images are shown below. Figure 4 , 5 In cases 6 and 7, the images of the microcapsules from all three embodiments were similar, and there was no indication of microcapsule aggregation. This indicates that the presence of ubiquinone-10 does not affect the quality of the microcapsules.

[0132] IV. Preparation of Microencapsulated Slurry

[0133] Example 5C1 Adjust the pH of the sieved microcapsule solution prepared in Example 5B to 9, and allow the microcapsules to settle by gravity or centrifugation. After settling, remove excess water. Add a poly(vinyl alcohol) binder solution (19% aqueous solution) to the concentrated capsule dispersion at a concentration of 60 mg per gram of microcapsules. Mix the resulting slurry overnight.

[0134] Comparative Example 6C1The preparation process of the microcapsule slurry in Example 5C was repeated using the sieved microcapsule solution prepared in Comparative Example 6B.

[0135] Example 7C1 The preparation process of the microcapsule slurry in Example 5C was repeated using the sieved microcapsule solution prepared in Example 7B.

[0136] Comparative Example 8C1 The preparation process of the microcapsule slurry in Example 5C was repeated using the sieved microcapsule solution prepared in Comparative Example 5B.

[0137] Comparative Example 9C1 The preparation process of the microcapsule slurry in Example 5C was repeated using the sieved microcapsule solution prepared in Comparative Example 9B.

[0138] Example 5C2 Repeat the preparation process of the microcapsule slurry in Example 5C1, but replace the poly(vinyl alcohol) solution with a polyurethane dispersion.

[0139] Example 6C2 Repeat the preparation process of the microcapsule slurry in Example 6C1, but replace the poly(vinyl alcohol) solution with a polyurethane dispersion.

[0140] V. Fabrication of Color Electro-optic Displays

[0141] Example 5D The slurry prepared in Example 5C1 was bar-coated onto a 127-micrometer-thick polyester film coated with indium tin oxide (ITO), which served as the first electrode layer. The coated film was oven-dried to produce a film with a thickness of approximately 30 micrometers. The film essentially consisted of a monolayer of microcapsules on ITO. A front panel laminate was prepared from the resulting film by laminating a polyurethane adhesive onto the capsule layer (see U.S. Patent No. 6,982,178). The front panel laminate was then laminated onto a segmented graphite backing plate, which contained a graphite layer on a polyester film, to produce a color electro-optic display suitable for measuring its electro-optic properties. The color electro-optic display was equilibrated at 25°C and 50% relative humidity for five days.

[0142] Comparative Example 6D The preparation process of the electro-optic display of Example 5D was repeated using the slurry from Comparative Example 6C1.

[0143] Example 7D The preparation process of the electro-optic display of Example 5D was repeated using the slurry from Example 7C1.

[0144] Comparative Example 8D The preparation process of the electro-optic display of Example 5D was repeated using the slurry from Comparative Example 8C1.

[0145] Comparative Example 9DThe preparation process of the electro-optic display of Example 5D was repeated using the slurry from Comparative Example 9C1.

[0146] Example 5E The preparation process of the electro-optic display of Example 5D was repeated using the slurry from Example 5C2.

[0147] Comparative Example 6E The preparation process of the electro-optic display of Example 5D was repeated using the slurry from Comparative Example 6C2.

[0148] VI. Evaluation of the lightfastness of color electro-optic displays.

[0149] The lightfastness of color optoelectronic displays from Examples 5D, 6D, 7D, 8D, 9D, 5E, and 6E was evaluated by illuminating one half of each display while keeping the other half opaque. The opaque half served as a control for the exposed portion of the display. The experiments were conducted in an environment with controlled temperature and humidity. The evaluation involved the following steps: (a) placing the display in a chamber with a relative humidity of approximately 50% and a temperature of approximately 25°C, and (b) illuminating one half of the display with D65 (6500K) CIE, which roughly corresponds to the average midday light in Western / Northern Europe (including direct sunlight and diffused light from a clear sky), and is therefore referred to as a daylight source.

[0150] The color gamut of each color electro-optical display was measured according to the electro-optical testing procedures described in the next section. An arbitrary assessment value of the display's lightfastness was calculated by comparing the percentage of gamut loss, normalized to the exposed and unexposed areas, relative to the exposed values. Panels with a smaller gamut loss percentage were considered to have higher lightfastness.

[0151] VII. Evaluation Methods for Electro-optic Properties

[0152] Electro-optic displays from Examples 5D, 6D, 5E, 6E, 7D, 8D, and 9D were electrically driven to generate eight optical states. An electrophoresis apparatus was addressed using a sequence of electrical pulses (such a sequence is referred to as a "waveform"). In the following description, the voltage used in the waveforms is the voltage supplied to the rear electrode of the display, assuming that the front (viewing) electrode of the display is the first electrode of all pixels and grounded. The color states of the displays were recorded (measured in CIELab L*, a*, and b* units). The color gamut of each display was measured by calculating the convex hull volume containing each color state generated by the test waveform set. Type I electrophoretic media correspond to Examples 5A and 6A. Type II electrophoretic media correspond to Examples 7A, 8A, and 9A. The evaluation results of the electro-optic performance are summarized in Table 1.

[0153]

[0154]

[0155] The results clearly show that the introduction of the electron acceptor ubiquinone-10 into the electrophoretic medium reduces the gamut loss caused by light exposure, expressed as a percentage of gamut loss in Table 1. Furthermore, Table 1 shows that the addition of the electron donor ubiquinol-10 (the reduced form of ubiquinone-10) to the electrophoretic medium has an adverse effect on the lightfastness of the color electro-optic display. The beneficial effect of the electron acceptor was observed for both different types of electrophoretic displays (Type I and Type II) and also for both different types of adhesives (polyvinyl alcohol and polyurethane).

Claims

1. A color electro-optical display, comprising, in sequence: The first electrode layer includes a light-transmitting electrode; An electro-optic material layer comprising an electrophoretic medium encapsulated in a plurality of microunits or microcapsules, the electrophoretic medium comprising a plurality of first-type charged pigment particles, a plurality of second-type charged pigment particles, a lightfastness additive, and a nonpolar liquid, the lightfastness additive being an electron acceptor and present in the electrophoretic medium at a content of 0.1% to 6.0% by weight. The second electrode layer includes multiple pixel electrodes.

2. The color electro-optic display of claim 1, wherein the lightfastness additive is selected from substituted 1,4-benzoquinone, substituted 1,2-benzoquinone, substituted naphthoquinone, and substituted anthraquinone, wherein the substituted 1,4-benzoquinone, the substituted 1,2-benzoquinone, the substituted naphthoquinone, and the substituted anthraquinone have at least one substituent comprising an alkyl, cycloalkyl, or alkenyl group, and wherein the at least one substituent has 10 to 120 carbon atoms.

3. The color electro-optic display of claim 2, wherein the substituted 1,2-benzoquinone, the substituted 1,4-benzoquinone, the substituted naphthoquinone, and the substituted anthraquinone have at least one substituent, the at least one substituent being represented by formula I or formula II, wherein n is an integer from 2 to 20, and wherein m is an integer from 1 to 20.

4. The color electro-optic display of claim 2, wherein the lightfastness additive is a substituted 1,4-benzoquinone represented by formula III. R1 is represented by formula I or formula II, where n is an integer from 2 to 20 and m is an integer from 1 to 20, and where R2 to R4 are independently selected from hydrogen, alkyl groups, alkenyl groups, aryl groups and heteroatom groups containing heteroatoms of groups V-VII of the periodic table.

5. The color electro-optic display of claim 4, wherein R1 is represented by formula II, m is an integer from 2 to 20, and wherein each of R2, R3 and R4 is independently selected from hydrogen, alkyl, alkenyl and alkoxy groups.

6. The color electro-optic display of claim 5, wherein R2 is a methyl group, and wherein R3 and R4 are methoxy groups.

7. The color electro-optic display of claim 5, wherein R2 is hydrogen, and wherein R3 and R4 are methyl groups.

8. The color electro-optic display of claim 7, wherein the lightfast additive is represented by formula IV or formula V. 。 9. The color electro-optic display of claim 2, wherein the molecular structure of the lightfastness additive is a substituted benzoquinone represented by formula VI. ， Each of R5, R6 and R7 may be independently selected from hydrogen, alkyl, alkenyl and alkoxy groups, and o is an integer from 2 to 20.

10. The color electro-optic display of claim 2, wherein the lightfastness additive is a substituted naphthoquinone, the substituted naphthoquinone being represented by formula VII. Among them, R8, R9, R 10 R 11 and R 12 Each of them may be independently selected from hydrogen, alkyl, alkenyl and alkoxy groups, and wherein p is an integer from 2 to 20.

11. The color electro-optic display of claim 2, wherein the lightfastness additive is a substituted naphthoquinone, the substituted naphthoquinone being represented by formula VIII. Where R 13 R 14 R 15 R 16 and R 17 Each of the groups can be independently selected from hydrogen, alkyl, alkenyl and alkoxy groups, and q is an integer from 2 to 20.

12. The color electro-optic display of claim 11, wherein the molecular structure of the lightfastness additive is represented by formula VIII, wherein R 13 R 14 R 15 R 16 It is hydrogen, and R 17 It is a methyl group.

13. The color electro-optical display of claim 12, wherein q is selected from 3, 4, 7 and 9.

14. The color electro-optic display according to any one of claims 1 to 13, wherein the electrophoretic medium further comprises a plurality of third-type charged pigment particles and a plurality of fourth-type charged pigment particles.

15. The color electro-optic display of claim 14, wherein the charged pigment particles of the first, second, third and fourth types have colors selected from white, black, cyan, magenta, yellow, blue, green and red.

16. The color electro-optic display of claim 14, wherein the charged pigment particles of the first, second, third, and fourth types are white, cyan, magenta, and yellow, respectively.

17. The color electro-optic display according to any one of claims 1 to 16, wherein the electro-optic material layer comprises a plurality of microcapsules and an adhesive.

18. The color electro-optic display of claim 17, wherein the color electro-optic display further comprises a first adhesive layer disposed between the electro-optic material layer and the second electrode layer.

19. The color electro-optic display of claim 18, wherein the color electro-optic display further comprises a second adhesive layer disposed between the electro-optic material layer and the first electrode layer.

20. The color electro-optic display according to any one of claims 1 to 16, wherein the electro-optic material layer comprises a plurality of micro-units, each of the plurality of micro-units having a micro-unit bottom, a partition wall, an opening, and a sealing layer extending across the opening, the sealing layer being adjacent to the second electrode layer.

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