Patent Application
20250076688
This invention relates to an electro-optic device comprising an electrophoretic medium including electrically charged pigment particles, an organic electroactive compound, and a non-polar liquid. The electrophoretic medium is included in a plurality of microcells. The composition of the electrophoretic medium enables the reduction of remnant voltage of the electro-optic device even after operation using DC-imbalance waveform.
The terms “bistable” and “bistability” are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display forms differing in at least one optical property, and such that after any given element has been driven, by means of an addressing pulse of finite duration, to assume either its first or second display form, after the addressing pulse has terminated, that 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. It is shown in U.S. Pat. No. 7,170,670 that some particle-based electrophoretic displays capable of gray scale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true of some other types of electro-optic displays. This type of display is properly called “multi-stable” rather than bistable, although for convenience the term “bistable” may be used herein to cover both bistable and multi-stable displays.
The term “electro-optic”, as applied to a material or a display, is used herein in its conventional meaning in the imaging art to refer to a material having first and second display states differing in at least one optical property, the material being changed from its first to its second display state by application of an electric field to the material. Although the optical property is typically color perceptible to the human eye, it may be another optical property, such as optical transmission, reflectance, luminescence or, in the case of displays intended for machine reading, pseudo-color in the sense of a change in reflectance of electromagnetic wavelengths outside the visible range.
Some electro-optic media are solid in the sense that the materials have solid external surfaces, although the media may, and often do, have internal liquid filled or gas filled spaces. Displays using solid electro-optic media may hereinafter for convenience be referred to as “solid electrophoretic displays”.
Several types of electro-optic displays are known. One type of electro-optic display is a rotating bichromal member type as described, for example, in U.S. Pat. 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 bichromal ball” display, the term “rotating bichromal member” is preferred as more accurate since in some of the patents mentioned above the rotating members are not spherical). Such a display uses a large number of small bodies (typically spherical or cylindrical) which have two or more sections with differing optical characteristics, and an internal dipole. These bodies are suspended within liquid filled vacuoles within a matrix, the vacuoles being filled with liquid so that the bodies are free to rotate. The appearance of the display is changed by applying an electric field thereto, thus rotating the bodies to various positions and varying which of the sections of the bodies is seen through a viewing surface. This type of electro-optic medium is typically bistable.
Another type of electro-optic display uses an electrochromic medium, for example an electrochromic medium in the form of a nanochromic film comprising an electrode formed at least in part from a semi-conducting metal oxide and a plurality of dye molecules capable of reversible color change 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. Nanochromic films of this type are also described, for example, in U.S. Pat. Nos. 6,301,038; 6,870,657; and 6,950,220. This type of medium is also typically bistable.
Another type of electro-optic display is an electro-wetting display developed by Philips and described in Hayes, R. A., et al., “Video-Speed Electronic Paper Based on Electrowetting”, Nature, 425, 383-385 (2003). It is shown in U.S. Pat. No. 7,420,549 that such electro-wetting displays can be made bistable.
One type of electro-optic display, which has been the subject of intense research and development for a number of years, is the particle-based electrophoretic display, in which a plurality of electrically charged pigment particles move through a liquid under the influence of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread usage. For example, particles that make up electrophoretic displays tend to settle, resulting in inadequate service life for these displays.
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 gaseous fluids; 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. Pat. Nos. 7,321,459 and 7,236,291. Such gas-based electrophoretic media appear to be susceptible to the same types of problems due to particle settling as liquid-based electrophoretic media, when the media are used in an orientation which permits such settling, for example in a sign where the medium is disposed in a vertical plane. Indeed, particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based ones, since the lower viscosity of gaseous suspending fluids as compared with liquid ones allows more rapid settling of the electrophoretic particles.
Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various technologies used in encapsulated electrophoretic and other electro-optic media. Such encapsulated media comprise numerous small capsules, each of which itself comprises an internal phase containing electrophoretically mobile particles in a liquid, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes. The technologies described in the these patents and applications include:
Many of the aforementioned patents and applications recognize that the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium could be replaced by a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic medium and a continuous phase of a polymeric material, and that the discrete droplets of electrophoretic medium within such a polymer-dispersed electrophoretic display may be regarded as capsules or microcapsules even though no discrete capsule membrane is associated with each individual droplet; see for example, the aforementioned U.S. Pat. No. 6,866,760. Accordingly, for purposes of the present application, such polymer-dispersed electrophoretic media are regarded as sub-species of encapsulated electrophoretic media.
A related type of electrophoretic display is a so-called “microcell electrophoretic display”. In a microcell electrophoretic display, the electrically charged pigment particles and the fluid are not encapsulated within microcapsules but instead are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film. See, for example, U.S. Pat. Nos. 6,672,921 and 6,788,449, both assigned to Sipix Imaging, Inc.
Although electrophoretic media are often opaque (since, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called “shutter mode” in which one display state is substantially opaque and one is light transmissive. See, for example, U.S. Pat. Nos. 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely upon variations in electric field strength, can operate in a similar mode; see U.S. Pat. No. 4,418,346. Other types of electro-optic displays may also be capable of operating in shutter mode. Electro-optic media operating in shutter mode may be useful in multi-layer structures for full color displays; in such structures, at least one layer adjacent the viewing surface of the display operates in shutter mode to expose or conceal a second layer more distant from the viewing surface.
An encapsulated electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. Use of the word “printing” is intended to include all forms of printing and coating, including, but without limitation: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; ink jet printing processes; electrophoretic deposition (See U.S. Pat. No. 7,339,715); and other similar techniques. Thus, the resulting display can be flexible. Further, because the display medium can be printed using a variety of methods, the display itself can be made inexpensively.
An electro-optic display normally comprises a layer of electro-optic material and at least two other layers disposed on opposed sides of the electro-optic material, one of these two layers being an electrode layer. In most such displays both the layers are electrode layers, and one or both of the electrode layers are patterned to define the pixels of the display. For example, one electrode layer may be patterned into elongate row electrodes and the other into elongate column electrodes running at right angles to the row electrodes, the pixels being defined by the intersections of the row and column electrodes. Alternatively, and more commonly, one electrode layer has the form of a single continuous electrode, and the other electrode layer is patterned into a matrix of pixel electrodes, each of which defines one pixel of the display. In another type of electro-optic display, which is intended for use with a stylus, print head or similar movable electrode separate from the display, only one of the layers adjacent the electro-optic layer comprises an electrode, the layer on the opposed side of the electro-optic layer typically being a protective layer intended to prevent the movable electrode damaging the electro-optic layer.
The manufacture of a three-layer electro-optic display normally involves at least one lamination operation. For example, in several of the aforementioned MIT and E Ink patents and applications, there is described a process for manufacturing an encapsulated electrophoretic display in which an encapsulated electrophoretic medium comprising capsules in a binder is coated on to a flexible substrate comprising indium-tin-oxide (ITO) or a similar conductive coating (which acts as one electrode of the final display) on a plastic film, the capsules/binder coating being dried to form a coherent layer of the electrophoretic medium firmly adhered to the substrate. Separately, a backplane, containing an array of pixel electrodes and an appropriate arrangement of conductors to connect the pixel electrodes to drive circuitry, is prepared. To form the final display, the substrate having the capsule/binder layer thereon is laminated to the backplane using a lamination adhesive. (A very similar process can be used to prepare 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, over which the stylus or other movable electrode can slide.) In one preferred form of such a process, the backplane is itself flexible and is prepared by printing the pixel electrodes and conductors on a plastic film or other flexible substrate. The obvious lamination technique for mass production of displays by this process is roll lamination using a lamination adhesive. Similar manufacturing techniques can be used with other types of electro-optic displays. For example, a microcell electrophoretic medium or a rotating bichromal member medium may be laminated to a backplane in substantially the same manner as an encapsulated electrophoretic medium.
As discussed in the aforementioned U.S. Pat. No. 6,982,178, (see column 3, lines 63 to column 5, line 46) many of the components used in solid electro-optic displays, and the methods used to manufacture such displays, are derived from technology used in liquid crystal displays (LCD's), which are of course also electro-optic displays, though using a liquid rather than a solid medium. For example, solid electro-optic displays may make use of an active matrix backplane comprising an array of transistors or diodes and a corresponding array of pixel electrodes, and a “continuous” front electrode (in the sense of an electrode which extends over multiple pixels and typically the whole display) on a transparent substrate, these components being essentially the same as in LCD's. However, the methods used for assembling LCD's cannot be used with solid electro-optic displays. LCD's are normally assembled by forming the backplane and front electrode on separate glass substrates, then adhesively securing these components together leaving a small aperture between them, placing the resultant assembly under vacuum, and immersing the assembly in a bath of the liquid crystal, so that the liquid crystal flows through the aperture between the backplane and the front electrode. Finally, with the liquid crystal in place, the aperture is sealed to provide the final display.
This LCD assembly process cannot readily be transferred to solid electro-optic displays. Because the electro-optic material is solid, it must be present between the backplane and the front electrode before these two integers are secured to each other. Furthermore, in contrast to a liquid crystal material, which is simply placed between the front electrode and the backplane without being attached to either, a solid electro-optic medium normally needs to be secured to both; in most cases the solid electro-optic medium is formed on the front electrode, since this is generally easier than forming the medium on the circuitry-containing backplane, and the front electrode/electro-optic medium combination is then laminated to the backplane, typically by covering the entire surface of the electro-optic medium with an adhesive and laminating under heat, pressure and possibly vacuum. Accordingly, most prior art methods for final lamination of solid electrophoretic displays are essentially batch methods in which (typically) the electro-optic medium, a lamination adhesive and a backplane are brought together immediately prior to final assembly, and it is desirable to provide methods better adapted for mass production.
The aforementioned U.S. Pat. No. 6,982,178 describes a method of assembling a solid electro-optic display (including an encapsulated electrophoretic display) which is well adapted for mass production. Essentially, this patent describes a so-called “front plane laminate” (“FPL”) which comprises, in order, a light transmissive electrically conductive layer; a layer of a solid electro-optic medium in electrical contact with the electrically conductive layer; an adhesive layer; and a release sheet. Typically, the light transmissive electrically conductive layer will be carried on a light transmissive substrate, which is preferably flexible, in the sense that the substrate can be manually wrapped around a drum (say) 10 inches (254 mm) in diameter without permanent deformation. The term “light transmissive” is used in this patent and herein to mean that the layer thus designated transmits sufficient light to enable an observer, looking through that layer, to observe the change in display states of the electro-optic medium, which will normally be viewed through the electrically conductive layer and adjacent substrate (if present); in cases where the electro-optic medium displays a change in reflectivity at non-visible wavelengths, the term “light transmissive” should of course be interpreted to refer to transmission of the relevant non-visible wavelengths. The substrate will typically be a polymeric film, and will normally have a thickness in the range of about 1 to about 25 mil (25 to 634 μm), preferably about 2 to about 10 mil (51 to 254 μm). The electrically conductive layer is conveniently a thin metal or metal oxide layer of, for example, aluminum or ITO. The electrically conductive layer may comprise a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are available commercially, for example as “aluminized Mylar” (“Mylar” is a Registered Trademark) from E.I. du Pont de Nemours & Company, Wilmington DE, and such commercial materials may be used with good results in the front plane laminate.
Assembly of an electro-optic display using such a front plane laminate may be effected by removing the release sheet from the front plane laminate and contacting the adhesive layer with the backplane under conditions effective to cause the adhesive layer to adhere to the backplane, thereby securing the adhesive layer, layer of electro-optic medium and electrically conductive layer to the backplane. This process is well adapted to mass production since the front plane laminate may be mass produced, typically using roll-to-roll coating techniques, and then cut into pieces of any size needed for use with specific backplanes.
U.S. Pat. No. 7,561,324 describes a so-called “double release sheet” which is essentially a simplified version of the front plane laminate of the aforementioned U.S. Pat. No. 6,982,178. One form of the double release sheet comprises a layer of a solid electro-optic medium sandwiched between two adhesive layers, one or both of the adhesive layers being covered by a release sheet. Another form of the double release sheet comprises a layer of a solid electro-optic 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-optic display from a front plane laminate already described, but involving two separate laminations; typically, in a first lamination the double release sheet is laminated to a front electrode to form a front sub-assembly, and then in a second lamination the front sub-assembly is laminated to a backplane to form the final display, although the order of these two laminations could be reversed if desired.
U.S. Pat. No. 7,839,564 describes a so-called “inverted front plane laminate”, which is a variant of the front plane laminate described in the aforementioned U.S. Pat. No. 6,982,178. This inverted front plane laminate comprises, in order, at least one of a light transmissive protective layer and a light transmissive electrically conductive layer; an adhesive layer; a layer of a solid electro-optic medium; and a release sheet. This inverted front plane laminate is used to form an electro-optic display having a layer of lamination adhesive between the electro-optic layer and the front electrode or front substrate; a second, typically thin, layer of adhesive may or may not be present between the electro-optic layer and a backplane. Such electro-optic displays can combine good resolution with good low temperature performance.
In a high resolution display, each individual pixel must be addressable without interference from the addressing of adjacent pixels (whether or not the electro-optic medium used is bistable). One way to achieve this objective is to provide an array of non-linear elements, such as transistors or diodes, wherein at least one non-linear element is associated with each pixel, to produce an active matrix display, as mentioned above. An addressing (pixel) electrode, which addresses one pixel, is connected to an appropriate voltage source through its associated non-linear element. Conventionally, in high resolution arrays, the pixels are arranged in a two-dimensional array of rows and columns, such that any specific pixel is uniquely defined by the intersection of one specified row and one specified column. The sources of all the transistors in each column are connected to a single column electrode, while the gates of all the transistors in each row are connected to a single row electrode; the assignment of sources to rows and gates to columns is conventional and could be reversed if desired. The row electrodes are connected to a row driver, which essentially ensures that at any given moment only one row is selected, i.e., that there is applied to the selected row electrode a voltage such as to ensure that all the transistors in the selected row are conductive, while there is applied to all other rows a voltage such as to ensure that all the transistors in these non-selected rows remain non-conductive. The column electrodes are connected to column drivers, which place upon the various column electrodes voltages selected to drive the pixels in the selected row to their desired optical states. The aforementioned voltages are relative to a common front electrode, which is conventionally provided on the opposed side of the electro-optic medium from the non-linear array and extends across the whole display. After a pre-selected interval known as the “line address time” the selected row is deselected, the next row is selected, and the voltages on the column drivers are changed so that 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.
In the discussion below, the term “waveform” will be used to denote the entire voltage against time curve used to effect the transition of a pixel from one specific initial gray level to a specific final gray level. Typically such a waveform will comprise a plurality of waveform elements; where these elements are essentially rectangular (i.e., where a given element comprises application of a constant voltage for a period of time); the elements may be called “pulses” or “drive pulses”. The term “drive scheme” denotes a set of waveforms sufficient to effect all possible transitions between gray levels for a specific display. A display may make use of more than one drive scheme; for example, U.S. Pat. No. 7,012,600 teaches that a drive scheme may need to be modified depending upon parameters such as the temperature of the display or the time for which it has been in operation during its lifetime, and thus a display may be provided with a plurality of different drive schemes to be used at differing temperature etc. A set of drive schemes used in this manner may be referred to as “a set of related drive schemes.”
Prior art front electrodes for use with the electrophoretic and similar electro-optic displays typically comprise a very thin (about 0.1 μm) layer of a ceramic, such as indium tin oxide or a similar mixed metal oxide (see the aforementioned U.S. Pat. No. 6,982,178). This thin layer is normally formed by sputtering the ceramic on to a polymer film, typically poly(ethylene terephthalate). Prior art rear (pixel) electrodes may be formed in a similar manner, or may be formed from thin metal films; the front electrode must of course be light transmissive to enable the electro-optic layer to be seen, whereas with a reflective electro-optic layer, the rear electrodes can be opaque.
Although ceramic front electrodes have been in large scale commercial use for many years, they still suffer from a number of mechanical, optical and electrical problems. The tensions and temperatures used during lamination steps in the manufacture of the display may cause the ceramic to crack and form discontinuities in conductivity, leading to poor or inconsistent switching of the display. These cracks are also areas of high water vapor transmission, which may cause local damage to a humidity sensitive electro-optic medium (many of the aforementioned types of electro-optic media are sensitive to humidity). In color display using color filter arrays (CFA's), it is desirable to reduce parallax problems by bringing the CFA as close as possible to the electro-optic layer using a thin polymeric film, reducing the thickness of the PET substrate on which the ITO is coated. As the PET substrate is made thinner the cracking issues associated with the ITO are accentuated due to the higher thermal shrinkage of the thinner base.
As discussed in detail in the aforementioned U.S. Pat. No. 7,119,772, it has been found desirable for at least some types of electro-optic display that the drive scheme at each pixel location be DC balanced, in the sense that, for any series of transitions beginning and ending at the same gray level, the algebraic sum of the impulses applied during the series of transitions be bounded. It has been found that accurately DC-balanced waveforms (i.e., those in which the integral of current against time for any particular pixel of the display is held to zero over an extended period of operation of the display) are required to preserve image stability, maintain symmetrical switching characteristics, and provide the maximum useful working lifetime in certain displays of the prior art.
It is generally preferred that all individual waveforms within a drive scheme be DC balanced, but in practice this has been difficult to achieve. Thus, typical drive schemes have usually been a mixture of DC balanced and DC imbalanced waveforms, even though the drive scheme as a whole has been DC balanced.
As discussed in the aforementioned U.S. Pat. No. 7,119,772, the extent to which DC-imbalanced driving affects an electrophoretic or other electro-optic display (presumably by polarization of certain display components, as discussed in more detail below) may be ascertained by measuring the open circuit potential, hereinafter for convenience called the “remnant voltage”, of a particular region, such as a pixel, of the display. When the remnant voltage of a pixel is zero, it is taken to be DC balanced. If its remnant voltage is positive, it is taken to be DC unbalanced in the positive direction. If its remnant voltage is negative, it is taken to be DC unbalanced in the negative direction. Non-zero remnant voltages have been found to correlate with difficulties in accurate gray level placement.
The degradation in display performance caused by development of remnant voltage is generally reversible, either by storing the display without further switching or by switching appropriately to rebalance the DC impulses. In cases where a prior art electrophoretic display is driven with extreme degrees of DC-imbalance, however, it is possible that the electrodes may be irreversibly degraded, presumably by electrochemical reactions that consume the electrode materials.
Although DC-balanced driving waveforms effectively protect against development of remnant voltages and electrode degradation, there are problems associated with their use. Extra time must be allocated in order to provide balancing impulses, sometimes resulting in update times that are two to three times longer than would be possible with a DC-imbalanced drive. In some electrophoretic compositions, the time required for an optical transition from black to white is different from that required from white to black. In a DC-balanced waveform, the longer of the two switching times must be used for both transitions. In addition, distracting optical transitions may be visible to the user of the display during DC-balanced updates.
As described for example in U.S. Pat. Nos. 6,724,519 and 7,564,614, corrosion inhibitors may be incorporated into electro-optic displays to prevent damage to electrodes from DC imbalances during driving of the displays. U.S. Pat. Nos. 9,726,957, 10,520,786, and 11,513,414 disclosed an electrophoretic display having an electro-optic material comprising an encapsulated electrophoretic media and a polymer layer between the electro-optic material layer and an electrode, wherein the polymer layer comprises a redox compound. The redox material mitigates the degradation of the display components from DC-imbalances. The present invention provides a more effective alternative method of preventing damage by including an organic electroactive compound in the electrophoretic medium. The present invention also provides an effective method of reducing the remnant voltage of the 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. The organic electroactive compound is present in an oxidized form and a reduced form in the electrophoretic medium. Its reduced form is oxidizable at one of the electrodes and its oxidized form is reducible at one of the electrodes, preventing damage of the electrodes and other components of the device.
Accordingly, this invention provides an electro-optic device comprising a first electrode layer comprising a light transmissive electrode, a second electrode layer comprising a plurality of pixel electrodes, and a microcell layer, the microcell layer being 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 comprising an electrophoretic medium, the electrophoretic medium being in contact with the light transmissive electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium includes (a) electrically charged pigment particles, (b) a non-polar liquid, (c) a charge control agent, and (d) an organic electroactive compound. The organic electroactive compound is present in the electrophoretic medium in an oxidized form and a reduced form. The oxidized form of the organic electroactive compound is electrochemically reducible at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable at the surface of one of the first and second electrode layers. The oxidized form and the reduced form of the organic electroactive compound (i) are soluble in the non-polar liquid of the electrophoretic medium, or (ii) are included in reverse micelle structures that are present in the electrophoretic medium. The oxidized form of the organic electroactive compound may have a reduction potential that is not greater than 1.0 V relative to a standard hydrogen electrode.
The molecular structure of the reduced form of the organic electroactive compound may be represented by Formulas I to IX. R1 to R39 may be hydrogen, substituted or unsubstituted alkyl or aryl groups, and substituents R1 and R2, taken together, and/or R3 and R4, and/or R5 and R6, and/or R6 and R7, and/or R7 and R8, R9 and R10, and/or R11 and R12, and/or R14 and R15, and/or R15 and R16, and/or R16 and R17, and/or R19 and R20, and/or R21 and R22, and/or R25 and R26, and/or R26 and R27, and/or R27 and R28, may form a ring; and at least one of R31 and R32 is an aryl group, at least one of R33 and R34 is an aryl group, and at least one of R36 and R37 is an aryl group.
Groups R1 to R39 may be hydrogen, substituted or unsubstituted alkyl, alkenyl, or aryl groups. Substituents R1 and R2 (taken together), and/or R3 and R4, and/or R5 and R6, and/or R6 and R7, and/or R7 and R8, R9 and R10, and/or R11 and R12, and/or R14 and R15, and/or R15 and R16, and/or R16 and R17, and/or R19 and R20, and/or R21 and R22, and/or R25 and R26, and/or R26 and R27, and/or R27 and R28, may form a ring. At least one of R31 and R32 may be an aryl group, at least one of R33 and R34 is an aryl group, and at least one of R36 and R37 is an aryl group.
At least one of R1 to R4 of Formula I, at least one of R5 to R8 of Formula II, at least one of R9 to R13 of Formula III, at least one of R14 to R18 of formula IV, at least one of R19 to R24 of Formula V, at least one of R25 to R30 of Formula VI, at least one of R31 and R32 of Formula VII, at least one of R33 to R35 of Formula VIII, and at least one of R36 to R39 of Formula IX may be an alkyl or alkenyl group having at least 10 carbon atoms.
At least one of R9 to R12 of Formula III, at least one of R14 to R17 of formula IV, at least one of R19 to R22 of Formula V, at least one of R25 to R28 of Formula VI, at least one of R33 and R34 of Formula VIII, and at least one of R36 and R37 of Formula IX may be an alkyl or alkenyl group having at least 10 carbon atoms. The alkyl or alkenyl group may have from 10 to carbon atoms to 100 carbon atoms. The alkyl or alkenyl group comprises an isoprene dimer or oligomer may comprise from 1 to 20 isoprenyl units (—CH2CH═C(CH3)CH2—). The alkyl or alkenyl group may comprise an isoprene dimer or oligomer comprising from 1 to 13 isoprenyl units (—CH2CH═C(CH3)CH2—).
The molecular structure of the reduced form of the 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 be both methoxy groups, and R3 may be methyl group. Groups R1 and R2 may be both methyl groups, and R3 may be hydrogen.
The reduced form of the organic electroactive compound may be ubiquinol-10.
The reduced form of the organic electroactive compound may be represented by Formula XI.
The molecular structure of the oxidized form of the organic electroactive compound may be represented by Formula XII. Groups R40, R41, R42, R43, and R44 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and m may be an integer from 2 to 20.
The molecular structure of the oxidized form of the organic electroactive compound may be represented by Formula XIII or Formula XIV. Groups R45, R46, R47, R48, R49, R50, R51, and R52 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. Integer q may be selected from the group consisting of 3, 4, 7, and 9.
If the organic electroactive compound is represented by Formula XIV, groups R48, R49, R50, and R51 may all be hydrogens, and R52 may be methyl.
In another aspect, this invention provides a method of operating an electro-optic device, the method of operating comprising: (a) providing the electro-optic device; and (b) driving the electro-optic device using a DC-imbalanced waveform. The remnant voltage of the electro-optic device may be lower than the remnant voltage of a control electro-optic device, the control electro-optic device including a control electrophoretic medium comprising no organic electroactive compound. The electro-optic device comprises a first electrode layer comprising a light transmissive electrode, a second electrode layer comprising a plurality of pixel electrodes, and a microcell layer, the microcell layer being 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 comprising an electrophoretic medium, the electrophoretic medium being in contact with the light transmissive electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium includes (a) electrically charged pigment particles, (b) a non-polar liquid, (c) a charge control agent, and (d) an organic electroactive compound. The organic electroactive compound is present in the electrophoretic medium in an oxidized form and a reduced form. The oxidized form of the organic electroactive compound is electrochemically reducible at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable at the surface of one of the first and second electrode layers. The oxidized form and the reduced form of the organic electroactive compound are soluble in the non-polar liquid of the electrophoretic medium or are included in reverse micelle structures that are present in the electrophoretic medium.
According to another aspect, this invention provides an electro-optic device comprising a first electrode layer comprising a light transmissive electrode, a second electrode layer comprising a plurality of pixel electrodes, and a microcell layer, the microcell layer being 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 comprising an electrophoretic medium, the electrophoretic medium being in contact with the light transmissive electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium includes (a) electrically charged pigment particles, (b) a non-polar liquid, (c) a charge control agent, and (d) an organic electroactive compound. The organic electroactive compound is present in the electrophoretic medium in an oxidized form or a reduced form. The oxidized form of the organic electroactive compound is electrochemically reducible at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable at the surface of one of the first and second electrode layers. The oxidized form and the reduced form of the organic electroactive compound (i) are soluble in the non-polar liquid of the electrophoretic medium, or (ii) are included in reverse micelle structures that are present in the electrophoretic medium. The oxidized form of the organic electroactive compound may have a reduction potential that is not greater than 1.0 V relative to a standard hydrogen electrode.
The term “oxidized form” referring to an organic electroactive compound is used herein to include the fully oxidized form of the organic electroactive compound and other molecules that are more oxidized than the fully reduced form of the organic electroactive compound. The term “reduced form” referring to an organic electroactive compound is used herein to include the fully reduced form of the organic electroactive compound and other compounds that are more reduced than the fully oxidized form of the organic electroactive compound.
The term “unsubstituted alkyl group” refers to branched and unbranched group containing one or more single C—C bonds, and not a double C—C bond or a triple C—C bond. The term “unsubstituted alkyl group” includes cyclic groups containing single C—C bonds and not a double C—C bond or a triple C—C bond or an aromatic group. The term “unsubstituted alkenyl group” refers to branched and unbranched groups containing one or more double C—C bonds. The term “unsubstituted aryl group” refers to a group containing an aromatic ring. The term “substituted alkyl group” refers to an alkyl group, in which one or more hydrogen is replaced by a substituent, the substituent not being an alkyl group. The substituent may be an alkenyl group, an aryl group, or a group that includes a heteroatom, the heteroatom being an atom of groups V-VII of the periodic table. The term “substituted alkenyl” refers to an alkenyl group, in which one or more hydrogen is replaced by a substituent, the substituent not being an alkenyl group or an alkyl group. The substituent may be an aryl group or a group that includes a heteroatom, the heteroatom being an atom of groups V-VII of the periodic table. The term “substituted aryl” refers to an aryl group, in which one or more hydrogen is replaced by a substituent. The substituent may be an alkyl group, an alkenyl group, an aryl group or a group that comprises a heteroatom, the heteroatom being an atom of groups V-VII of the periodic table. Non-limiting examples of heteroatom are nitrogen, phosphorus, oxygen, sulfur, selenium, fluorine, chlorine, bromine, and iodine. Non-limiting examples of groups that comprises a heteroatom are hydroxyl, amino, alkoxy, carboxy, thio, cyano, nitro, and others.
A typical electro-optic display may have an electro-optic material layer that comprise electrophoretic medium, which is encapsulated in microcapsules or microcells, as described in U.S. Pat. No. 6,982,178.
In the electro-optic display of
In the electro-optic displays of
The electrophoretic medium of electro-optic display 100 of
As described in U.S. Pat. No. 6,982,178, adhesive layer 110 of the electrophoretic medium of electro-optic display 100 is disposed between electro-optic material layer 108, which comprises encapsulated electrophoretic medium, and the plurality of pixel electrodes 112 of backplane 118 (see
Adhesive layer 110 of the microcapsule electro-optic display 100 of
Polymeric layer 106 of microcapsule electro-optic display 100 of
Species A refers to any mobile, positively charged species in polymeric layer 106. Likewise, species E and F refer to positively charged and negatively charged mobile species in adhesive layer 110. Species C and D refer to mobile, charged entities in the electrophoretic medium of electro-optic material layer 108; such entities include charged pigment particles, whose motion changes the optical state of the display, and charged species, whose motion has no direct optical effect, such as micellar charges that are well known in the art.
Charged species may cross the boundaries between the various layers of the display. This is shown schematically in
Even if mobile ionic charges can flow freely across the boundaries between the layers within the display (without accumulating at the internal boundaries), there is still the difficulty that ionic species cannot cross the boundaries between the interior layers of the display and the electrodes 104 and 112. The only likely 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 interior layers is blocked, ionic charges will inevitably build up at the boundaries between electrode 104 and layer 106 and between layer 110 and electrode 112. If the display is driven with a DC imbalanced drive scheme a substantial charge build-up at these locations may occur. Relaxation of the built-up charge when the electrodes are brought to a common potential may lead to a flow of charge carriers through the electro-optic material layer 108. This flow of charge carriers may lead to a change in the optical state of the display, which may be undesirable.
The above-mentioned U.S. Pat. No. 9,726,957 disclosed a technology that mitigates the problem of charge accumulation by adding an electrochemically active compound into a layer of the electro-optic display that is adjacent to the electro-optic material layer. The electrochemically active compound is oxidizable or reducicble. The invention of U.S. Pat. No. 9,726,957 is schematically illustrated in
As mentioned above, in the above-mentioned U.S. Pat. No. 9,726,957, the electrochemically active compound that is used to control charge injection at the electrode interface is incorporated into an external phase layer of the display, that is, in a layer different from the electro-optic material layer, which includes the electrophoretic medium. However, it was found that, in practice, only those components that are within a sufficiently short distance from effective electron transfer to or from the electrodes would be effectively oxidized or reduced. Thus, the components undergoing electron transfer at an electrode might be depleted faster than the time required to be replenished by diffusion onto the electrode surface, given that diffusion of typical electroactive compounds through polymers are too slow to sustain a practical electric current in the display. For this reason, the electro-optic device structure disclosed in U.S. Pat. No. 9,726,957 is not optimal to mitigate the problem of charge accumulation at the electrodes and the resulting remnant voltage.
The inventors of the present invention surprisingly found that a microcell elector-optic device having an electrophoretic medium in contact with the first electrode layer and at least one of a plurality of pixel electrodes, the electrophoretic material comprising an organic electroactive compound, provides an effective mitigation of remnant voltage following extended DC-imbalanced driving. In another example, an electrophoretic medium in contact with the first electrode layer and all of the pixel electrodes of 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 comprising an electrophoretic medium, the electrophoretic medium being in contact with the light transmissive electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer (or more than one, or all, the pixel electrodes of the second electrode layer). The electrophoretic medium includes (a) electrically charged pigment particles, (b) a non-polar liquid, (c) a charge control agent, and (d) an organic electroactive compound. The organic electroactive compound is present in the electrophoretic medium in an oxidized form and a reduced form. The oxidized form of the organic electroactive compound is electrochemically reducible at the surface of one of the light transmissive electrodes of the first electrode layer and a pixel electrode of second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable at the surface of one of the light transmissive electrodes of the first electrode layer and a pixel electrode of the second electrode layer. The oxidized form and the reduced form of the organic electroactive compound are soluble in the non-polar liquid of the electrophoretic medium. Alternatively, the oxidized form and the reduced form of the organic electroactive compound are included in reverse micelle structures that are present in the electrophoretic medium.
The content of the organic electroactive compound in the electrophoretic medium may be from 0.1 to 10 weight percent by weight of the electrophoretic medium. The content of the organic electroactive compound in the electrophoretic medium may be from 0.2 to 8 weight percent, 0.3 to 6 weight percent, from 0.4 to 5 weight percent, from 0.5 to 4 weight percent, from 0.6 to 3 weight percent, or from 0.7 to 2 weight percent by weight of the electrophoretic medium.
Reverse micelle structures in a non-polar liquid (first liquid) are droplets of a second liquid or droplets of a dispersion (particles in a third liquid) that are surrounded by amphiphilic molecules. The droplets form the core of the reverse micelle structures. Amphiphilic molecules are molecules having both a hydrophobic group (head) and a hydrophobic group (tail) in their molecular structure. Typically, the beads of the amphiphilic molecules are oriented towards the core of each reverse micelle structure and the tails are oriented towards the outside surface of the reverse micelle structure, as the tails are hydrophobic and more compatible with the non-polar liquid. The second liquid or the third liquid are less hydrophobic than the tail of the amphiphilic molecule and the non-polar fluid and more compatible with the head of the amphiphilic molecule. The non-polar liquid is called “continuous phase” of the reverse micelle structures/non-polar liquid mixture.
Front substrate 202 of electro-optic device 300 of
The light transmissive electrode of first electrode layer 204 of electro-optic device 300 of
The electrophoretic medium of electro-optic display 300 of
The electrophoretic medium of electro-optic display 300 of
During the operation of the electro-optic device, the organic electroactive compound may be present in the electrophoretic medium in an oxidized form and in a reduced form. The oxidized form of the organic electroactive compound is electrochemically reducible at the surface, or near the surface, of the light transmissive electrode of the first electrode layer or a pixel electrode of the second electrode layer. The reduced form of the organic electroactive compound is electrochemically oxidizable at the surface, or near the surface, of the light transmissive electrode of the first electrode layer or a pixel electrode of the second electrode layer. That is, the oxidized form is electrochemically reversibly reduced to the reduced form and the reduced form is electrochemically reversibly oxidized to the oxidized form. The conversion of the oxidized form to the reduced form and from the reduced form to the oxidized form via redox reactions. Thus, organic electrochemically active compounds may also be called redox materials.
Although organic electroactive compounds that are capable of at least partial reversible redox reactions are preferred to those undergoing irreversible reactions, the ability to undergo fully reversible redox reactions is not an absolute requirement of the invention. The presence of the reduced form or the oxidized form of the organic electroactive compound at sufficient concentration mitigates premature degradation of the device and reduces the remnant voltage for a period of time.
A scheme that shows some important elements that are related to the operation of the electro-optic device of the invention, including the redox reactions at the electrodes is presented in
The organic electroactive compounds of the electrophoretic medium of the present invention are represented in
An electro-optic device must be able to be driven in both directions. That is, application of voltage of one polarity should cause migration of positively charged pigment particles to the viewing side, and application of voltage of the opposite polarity should cause migration of negatively charged pigment particles to the viewing side. In the present invention, a current can be sustained whichever polarity is used to address the device. That is, the protons formed at the anode will equilibrate with the negatively charged pigment particles and negatively charged reverse micelle structures that are driven to the anode, while protons are consumed at the cathode (or, equivalently, anionic materials that consume protons are formed at the cathode). Thus, the electrochemical reactions at the electrodes may at least partially neutralize the electrically charged pigment particles and the charged reverse micelle structures that have been migrated to the electrodes as the microcell is initially polarized. This charge neutralization may lead to a reduction in the remnant voltage that would otherwise cause electrical kick-back and image drift when the display is grounded after having been driven. Because electrical current may be sustained indefinitely in the electro-optic device of the present invention, there is no reason to expect that remnant voltage will increase substantially after an initial polarization and an establishment of a steady state. Indeed, the present inventors have surprisingly found that, in a model system, a current can pass through a microcell that contains organic electroactive compounds of the invention for 48 hours without a substantial increase in remnant voltage and without degradation of the electrodes.
Any compound that (a) has oxidized and reduced forms that may be at least partly reversibly formed and (b) is soluble, or can be part of reverse micelle structures, in the non-polar liquid of the electrophoretic medium may be used in the present invention. Preferred compounds include substituted quinone/hydroquinone pairs (or the corresponding catechols) in which side reactions are minimized by suitable substitution on the benzene ring or rings. One particularly preferred pair of compounds are ubiquinol/ubiquinone, having the structure shown in
It is possible that an electrophoretic medium of a device is initially charged with only one of the two forms (oxidized form or reduced form of a redox pair), because the corresponding partner compound will be formed as the device is driven. A reaction scheme of such formation is shown in
As mentioned above, the reduced form of the organic electroactive compound, which is 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.
The molecular structure of the reduced form of the organic electroactive compound may be represented by Formulas I to IX. In these formulas, R1 to R39 may be hydrogen, substituted or unsubstituted alkyl, alkenyl, or aryl groups, and substituents R1 and R2, taken together, and/or R3 and R4, and/or R5 and R6, and/or R6 and R7, and/or R7 and R8, R9 and R10, and/or R11 and R12, and/or R14 and R15, and/or R15 and R16, and/or R16 and R17, and/or R19 and R20, and/or R21 and R22, and/or R25 and R26, and/or R26 and R27, and/or R27 and R28, may form a ring; and at least one of R31 and R32 is an aryl group, at least one of R33 and R34 is an aryl group, and at least one of R36 and R37 is an aryl group.
At least one of R1 to R4 of Formula I, at least one of R5 to R8 of Formula II, at least one of R9 to R13 of Formula III, at least one of R14 to R18 of formula IV, at least one of R19 to R24 of Formula V, at least one of R25 to R30 of Formula VI, at least one of R31 and R32 of Formula VII, at least one of R33 to R35 of Formula VIII, and at least one of R36 to R39 of Formula IX may be an alkyl or alkenyl group having at least 10 carbon atoms.
At least one of R9 to R12 of Formula III, at least one of R14 to R17 of formula IV, at least one of R19 to R22 of Formula V, at least one of R25 to R28 of Formula VI, at least one of R33 and R34 of Formula VIII, and at least one of R36 and R37 of Formula IX may be an alkyl or alkenyl group having at least 10 carbon atoms. The alkyl or alkenyl group may have from 10 to carbon atoms to 100 carbon atoms. The alkyl or alkenyl group comprises an isoprene dimer or oligomer comprises from 1 to 20 isoprenyl units (—CH2CH═C(CH3)CH2—). The alkyl or alkenyl group may comprise an isoprene dimer or oligomer comprising from 1 to 13 isoprenyl units (—CH2CH═C(CH3)CH2—).
The molecular structure of the reduced form of the 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 be both methoxy groups, and R3 may be methyl group. Groups R1 and R2 may be both methyl groups, and R3 may be hydrogen.
The reduced form of the organic electroactive compound may be ubiquinol-10. The reduced form of the organic electroactive compound may be represented by Formula XI.
The molecular structure of the oxidized form of the organic electroactive compound may be represented by Formula XII. Groups R40, R41, R42, R43, and R44 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and m may be an integer from 2 to 20.
The molecular structure of the oxidized form of the organic electroactive compound may be represented by Formula XIII or Formula XIV Groups R40, R41, R42, R43, and R44 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. Integer q may be selected from the group consisting of 3, 4, 7, and 9. If the organic electroactive compound is represented by Formula XIV, groups R48, R49, R53, R50, and R51 may be hydrogens, and R52 may be methyl.
The oxidized form of the organic electroactive compound may have a reduction potential that is not greater than 1.0 V relative to a standard hydrogen electrode. Preferably, the oxidized form of the organic electroactive compound has a reduction potential that is not greater than 0.2 V relative to a standard hydrogen electrode. There are organic electroactive compounds meeting this reduction potential criterion, the organic electroactive compounds being soluble in the non-polar liquid of the electrophoretic medium, so that they can rapidly diffuse through the electrophoretic medium to participate in electrochemical reactions at the electrodes to reduce remnant voltages observed following extended DC-imbalanced driving.
It is believed, though the invention is in no way limited by this belief that, in the absence of an organic electroactive compound in accordance with the present invention, oxidation of water to form oxygen (a half-cell reaction with a standard reduction potential of more than 1 V) may occur. Because the organic electroactive compound used in the present invention is more easily reduced than water, when such organic electroactive compound is present, less ionic polarization is required to produce a sufficiently steep potential gradient in the electrode double layer for electron transfer to take place, and the remnant voltage experienced by the electro-optic material is consequently lower.
As mentioned above, the use of an organic electroactive compound in accordance with the present invention is intended to control the build-up of charge near the electrodes. Such a buildup of charge is typically a reversible process. The present invention also seeks to control the nature of the Faradaic reactions that occur at the electrode interfaces, so as to enable DC imbalanced driving of a display without incurring irreversible electrode damage. The organic electroactive compound of the present invention introduces a competitive redox pathway to allow Faradaic reactions to occur at the electrode interfaces without degradation of the electrodes. Without the use of the organic electroactive compound in accordance with the invention, unwanted Faradaic reactions may occur, such as electrolysis of water, leading to the formation of byproducts such as hydrogen and oxygen gas. Even worse, the electrode materials themselves may participate in redox reactions. Some materials that are used in transparent electrodes are prone to oxidation. For example, silver metal nanowires or grids may be readily oxidized to silver cations. Other materials that are widely used in transparent electrodes are prone to reduction. For example, conductive polymers, such as PEDOT:PSS, lose their conductivity when reduced. Indium tin oxide (ITO), another common material used in transparent electrodes, may be irreversibly reduced to metallic tin or metallic indium, leading to discoloration (yellowing) of the transparent electrodes and, eventually, to complete failure. The present invention seeks to introduce competitive redox chemistry to allow Faradaic reactions to occur at the electrode interfaces without degradation of the electrodes. In the case of ITO electrodes, it is desirable that the oxidized form of the organic electroactive compound used in the present invention is more easily reduced than ITO. That is, preferential reduction of the organic electroactive compound preserves the ITO electrode from irreversible electrochemical degradation. On the other hand, it is desirable that the oxidized form of the organic electroactive compound is not very easily reduced that it thermally oxidizes a reduced form, unless such an oxidation produces a new reduced form (i.e., the reduced form corresponding to the oxidized form).
The electro-optic device of the present invention may be operated by a method of operating that comprises the steps: (a) providing the electro-optic device; and (b) driving the electro-optic device using a DC-imbalanced waveform. The remnant voltage of the electro-optic device is reduced in comparison to the remnant voltage of a control electro-optic device.
A control electro-optic device is a device that comprises a control electrophoretic medium. A control electrophoretic medium is similar to an inventive electrophoretic medium in composition, but it does not comprise an organic electroactive compound. The inventive electro-optic device comprises a first electrode layer comprising a light-transmissive electrode, a second electrode layer comprising a plurality of pixel electrodes, and a microcell layer, the microcell layer being 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 comprising an electrophoretic medium, the electrophoretic medium being in contact with the light-transmissive electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer. The electrophoretic medium includes (a) electrically charged pigment particles, (b) a non-polar liquid, (c) a charge control agent, and (d) an organic electroactive compound. The organic electroactive compound is present in the electrophoretic medium in an oxidized form and a reduced form. The oxidized form of the organic electroactive compound is electrochemically reducible at the surface of one of the first and second electrode layers. The reduced form of the organic electroactive compound is electrochemically oxidizable at the surface of one of the first and second electrode layers. The oxidized form and the reduced form of the organic electroactive compound are soluble in the non-polar liquid of the electrophoretic medium or are included in reverse micelle structures that are present in the electrophoretic medium.
A solution was prepared containing (a) 1 weight % of charge control agents by weight of the solution, (b) 1 weight % of ubiquinol by weight of the solution, and (c) Isopar E. The charge control agent was prepared as described in Example 2 of U.S. Patent Application Pub. 2020/0355978. Ubiquinol-10 is supplied by Biosynth, Staad, Switzerland. The solution was introduced into a cell comprising two opposing glass plates, each coated with a transparent conductive coating of indium tin oxide (ITO) spaced apart by a distance of 25 μm, with a surface area of 6.5 cm2. The cell was sealed using an epoxy composition and then driven with 15V DC for 48 hours at 25° C. During the driving period, the electrical current that passed through the cell was continually measured. After this time, the cell was driven at 0V for 50 ms, following which it was allowed to float and the remnant voltage was measured.
The electric current flowing during the 48-hour driving period is provided in
An electrophoretic medium was prepared comprising a white pigment similar to pigment W1, a magenta pigment similar to pigment M1, and a cyan pigment similar to C1 in U.S. Pat. No. 10,678,111. The yellow pigment was a surface-treated Pigment Yellow 180, prepared by dispersion polymerization as described in Example 5 of U.S. Patent Application Pub. 2023/132958. The electrophoretic medium also contained the CCA of Example 1. The total amount of this CCA in the electrophoretic compositions was 1.8 weight % by weight of the electrophoretic medium. The electrophoretic medium also contained 1 weight % of polydimethylsiloxane polymer (PDMS DMS-T72 having molecular weight of approximately 700,000, supplied by Gelest Corporation) by weight of the electrophoretic medium as an image stabilizer. The weight % content of each pigment particle type by weight of the electrophoretic medium is shown in Table 1.
The electrophoretic medium from Example 2 was separated into two portions 2A and 2B. Sample 2A was loaded into a cell similar to that described above in Example 1, except that the distance between the two electrodes was 10 μm and the surface area was 1 cm2. Into Sample 2B ubiquinol and ubiquinone were added (1 weight % of ubiquinol by weight of the electrophoretic medium and 1 weight % of ubiquinol by weight of the electrophoretic medium) to prepare Sample 3B. Ubiquinol and Ubiquinone are available from AmBeed, IL, USA. Sample 3B was loaded into a cell (same type of cell as the one that Sample 2A was loaded). Cells containing Samples 2A and 3B were driven with DC voltages having amplitude of 1, 5, 15 and 30V. Each voltage was applied for 240 seconds, after which they were driven at 0V for 100 ms. Then, the cells were allowed to float while the remnant voltage was measured. FIG. 10 shows the currents measured for Samples 2A and 3B as a function of the applied voltage, while
The color gamut of the electro-optic device prepared from electrophoretic media of Sample 2A (control) and Sample 3B (inventive) were also measured. The waveform of
Clause 1: An electro-optic device comprising: a first electrode layer comprising a light-transmissive electrode; a second electrode layer comprising a plurality of pixel electrodes; a microcell layer disposed between the first electrode layer and the second electrode layer, the microcell layer comprising a plurality of microcells, each microcell of the plurality of microcells comprising an electrophoretic medium, the electrophoretic medium being in contact with the light-transmissive electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer, the electrophoretic medium including: (a) electrically charged pigment particles, (b) a non-polar liquid; (c) a charge control agent; and (d) an organic electroactive compound, wherein
Clause 2: The electro-optic device of clause 1, wherein the molecular structure of the reduced form of the organic electroactive compound is represented by Formulas I to IX, wherein R1 to R39 may be hydrogen, substituted or unsubstituted alkyl, alkenyl, or aryl groups, and substituents R1 and R2, taken together, and/or R3 and R4, and/or R5 and R6, and/or R6 and R7, and/or R7 and R8, R9 and R10, and/or R11 and R12, and/or R14 and R15, and/or R15 and R16, and/or R16 and R17, and/or R19 and R20, and/or R21 and R22, and/or R25 and R26, and/or R26 and R27, and/or R27 and R28, may form a ring; and at least one of R31 and R32 is an aryl group, at least one of R33 and R34 is an aryl group, and at least one of R36 and R37 is an aryl group.
Clause 3: The electro-optic device of clause 2, wherein at least one of R1 to R4 of Formula I, at least one of R5 to R8 of Formula II, at least one of R9 to R13 of Formula III, at least one of R14 to R18 of formula IV, at least one of R19 to R24 of Formula V, at least one of R25 to R30 of Formula VI, at least one of R31 and R32 of Formula VII, at least one of R33 to R35 of Formula VIII, and at least one of R36 to R39 of Formula IX is an alkyl or alkenyl group having at least 10 carbon atoms.
Clause 4: The electro-optic device of clause 2, wherein at least one of R9 to R12 of Formula III, at least one of R14 to R17 of formula IV, at least one of R19 to R22 of Formula V, at least one of R25 to R28 of Formula VI, at least one of R33 and R34 of Formula VIII, and at least one of R36 and R37 of Formula IX is an alkyl or alkenyl group having at least 10 carbon atoms.
Clause 5: The electro-optic device according to clause 3 or clause 4, wherein the alkyl or alkenyl group has from 10 to carbon atoms to 100 carbon atoms.
Clause 6: The electro-optic device according to any one of clause 2 to clause 5, wherein the alkyl or alkenyl group comprises an isoprene dimer or oligomer comprises from 1 to 20 isoprenyl units (—CH2CH═C(CH3)CH2—).
Clause 7: The electro-optic device according to any one of clause 2 to clause 5, wherein the alkyl or alkenyl group comprises an isoprene dimer or oligomer comprising from 1 to 13 isoprenyl units (—CH2CH═C(CH3)CH2—).
Clause 8: The electro-optic device according to any one of clause 2 to clause 7, wherein the molecular structure of the reduced form of the organic electroactive compound is represented by Formula X, wherein R1, R2, and R3 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and n is an integer from 2 to 20.
Clause 9: The electro-optic device of clause 8, wherein R1 and R2 are methoxy groups, and R3 is methyl group.
Clause 10: The electro-optic device of clause 9, wherein the reduced form of the organic electroactive compound is ubiquinol-10.
Clause 11: The electro-optic device of clause 8, wherein R1 and R2 are methyl groups, and R3 is hydrogen.
Clause 12: The electro-optic device of clause 11, wherein the reduced form of the organic electroactive compound is represented by Formula XI.
Clause 13: The electro-optic device according to clause 1, wherein the molecular structure of the oxidized form of the organic electroactive compound is represented by Formula XII, wherein R40, R41, R42, R43, and R44 may be hydrogen, alkyl, alkenyl, or alkoxy groups, and m is an integer from 2 to 20.
Clause 14: The electro-optic device of clause 1, wherein the molecular structure of the oxidized form of the organic electroactive compound is represented by Formula XIII or Formula XIV, wherein R45, R46, R47, R48, R49, R50, R51, and R52 may be hydrogen, alkyl, alkenyl, or alkoxy groups, p is an integer from 2 to 20, and q is an integer from 2 to 20.
Clause 15: The electro-optic device of clause 14, wherein the molecular structure of the oxidized form of the organic electroactive compound is represented by Formula XIV, R48, R49, R50, R51 are hydrogens, and R52 is methyl.
Clause 16: The electro-optic device of clause 15, wherein q is selected from the group consisting of 3, 4, 7, and 9.
Clause 17: The electro-optic device according to any one of clause 1 to clause 16, wherein the oxidized form of the organic electroactive compound has a reduction potential that is not greater than 1.0 V relative to a standard hydrogen electrode.
Clause 18: A method of operating an electro-optic device, the method of operating comprising: (a) providing the electro-optic device according to clause 1; and (b) driving the electro-optic device using a DC-imbalanced waveform.
Clause 19: The method of operating the electro-optic device of clause 18, wherein the remnant voltage of the electro-optic device is lower than the remnant voltage of a control electro-optic device, the control electro-optic device including a control electrophoretic medium comprising no organic electroactive compound.
Clause 20: An electro-optic device comprising: a first electrode layer comprising a light-transmissive electrode; a second electrode layer comprising a plurality of pixel electrodes; a microcell layer disposed between the first electrode layer and the second electrode layer, the microcell layer comprising a plurality of microcells, each microcell of the plurality of microcells comprising an electrophoretic medium, the electrophoretic medium being in contact with the light-transmissive electrode of the first electrode layer and at least one of the plurality of pixel electrodes of the second electrode layer, the electrophoretic medium including: (a) electrically charged pigment particles, (b) a non-polar liquid; (c) a charge control agent; and (d) an organic electroactive compound, wherein
This application claims priority to U.S. Provisional Patent Application No. 63/535,471 filed on Aug. 30, 2023, which is incorporated by reference in its entirety, along with all other patents and patent applications disclosed herein.
| Number | Date | Country | |
|---|---|---|---|
| 63535471 | Aug 2023 | US |
