Transition driving mode for impulse balancing when switching between global color mode and direct update mode of electrophoretic display

Abstract

A method of driving a multi-pixel electrophoretic display designed to allow at least three colors, e.g., eight, on each pixel. According to the method, a first driving scheme and a second driving scheme are adopted, the first driving scheme can achieve transition among all color states capable of being displayed on each pixel, and the second driving scheme only comprises transition ending with white or black. It is very useful for drawing black lines on a white page, reading black text on a white page, or reading white text on a black page. In order to control the amount of impulse potential accumulated for each pixel during switching between driving modes, two intermediate transition modes are added.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 401,110, filed on August 25, 2022. All patents and publications disclosed herein are incorporated herein by reference in their entirety. Background Art

[0003] An electrophoretic display (EPD) changes color by modifying the position of charged colored particles relative to a light-transmitting viewing surface. Such EPDs are often called "electronic paper" or "ePaper" because the resulting display has high contrast and is sunlight-readable, like ink on paper. EPDs have gained widespread adoption in e-readers, such as the Amazon Kindle®, because EPDs provide a book-like reading experience, consume little power, and allow users to carry a library of hundreds of books in a lightweight handheld device.

[0004] For many years, electrophoretic displays have included only two types of charged color particles, black and white. (It is to be understood that "color" as used herein includes both black and white.) The white particles are typically light-scattering and include, for example, titanium dioxide, while the black particles are absorptive in the visible spectrum and may include carbon black or an absorptive metal oxide such as copper chromite. In the simplest sense, a black-and-white electrophoretic display requires only a light-transmitting electrode at the viewing surface, a back electrode, and an electrophoretic medium including oppositely charged white and black particles. When a voltage of one polarity is provided, the white particles move to the viewing surface, and when a voltage of the opposite polarity is provided, the black particles move to the viewing surface. If the back electrode includes controllable areas (pixels) - segmented electrodes or an active matrix of pixel electrodes controlled by transistors - a pattern can be made to appear electronically at the viewing surface. The pattern can be, for example, text in a book.

[0005] Recently, multiple color options have become commercially available for electrophoretic displays, including three-color displays (black, white, red; black, white, yellow) and four-color displays (black, white, red, yellow). Similar to the operation of black and white electrophoretic displays, electrophoretic displays with three or four reflective particles operate similarly to simple black and white displays in that the desired color particles are driven to the viewing surface. The drive scheme is far more complex than just black and white, but ultimately, the optical function of the particles is the same.

[0006] Advanced Color Electronic Paper (ACEP®) also includes four particles, but the cyan, yellow, and magenta particles are subtractive rather than reflective, allowing thousands of colors to be produced at each pixel. The color process is functionally equivalent to the printing method long used in offset and inkjet printers. A given color is produced by using the correct ratio of cyan, yellow, and magenta on a bright white paper background. In the case of ACeP, the relative position of the cyan, yellow, magenta, and white particles with respect to the viewing surface will determine the color at each pixel. While this type of electrophoretic display allows thousands of colors to be displayed at each pixel, it is critical to carefully control the position of each of the (50 to 500 nanometers in size) pigments within a working volume that is approximately 10 to 20 microns thick. Obviously, variations in the particle position will result in an incorrect color being displayed at a given pixel. Therefore, such a system requires precise voltage control. Further details of the system may be found in the following U.S. patents, all of which are incorporated herein by reference in their entirety: U.S. Patent Nos. 9,361,836; 9,921,451; 10,276,109; 10,353,266; 10,353,266; 10,467,984; and 10,593,272.

[0007] Colors produced with such color electrophoretic displays may suffer from various "error accumulation" phenomena. These errors may be due to small perturbations in the drive voltage, accumulated residual voltage across a driven pixel, or temperature changes in the electrophoretic medium during a series of transitions. As a result, the desired color state may change due to accumulated voltage across a pixel and / or disturbances in the internal phase medium adjacent to that pixel. For example, after 100 consecutive color transitions in one area of ​​the display, a pixel returning to a black state may have an L* of 6, (where L* has the usual CIE definition:

[0008] L* = 116 (R / R0) 1 / 3 - 16,

[0009] where R is reflectance and R0 is the standard reflectance value), while another adjacent pixel does not change during these 100 consecutive transitions, starts and remains black, and after the same 100 transitions its L* is 4. For the average viewer, an L* deviation of 2 is noticeable and detracts from the overall experience of the display.

[0010] This error accumulation phenomenon applies to the color states as well as the black and white states. Again, due to the interaction of the electrophoretic particles, small changes in the local voltage or the electrophoretic medium environment may result in different colors being displayed on the display. In addition, for certain color states, especially in the case of yellow and green, the human eye is more sensitive to changes in chromaticity, and slight changes in color states may be perceived as unpleasant. For example, skin tones that appear greenish in hue may be very unpleasant to the viewer. Therefore, the general grayscale / color image flow requires very precise control of the applied impulses to give good results.

[0011] Further complicating matters, in some cases it may be desirable for a single display to be capable of using multiple drive schemes. For example, displays capable of producing multiple colors per pixel may typically operate in "Global Complete" (GC mode), where each color pixel has the ability to transition from a first color to a second color during each image update. Of course, as described in U.S. Patent No. 10,657,869, such updates may be time consuming (e.g., 1 second or more), especially when DC balancing and residual voltage management are required to achieve the highest quality color. However, in other instances, such as when drawing with a stylus or turning pages of text, very fast updates are required, and users are willing to sacrifice color fidelity in exchange for a faster update experience. This faster update scheme is often referred to as "Direct Update" ("DU mode"), and typically requires only driving the electrophoretic medium to the black and white extremes. See, for example, U.S. Patent No. 9,672,766. For higher-end end products, such as color e-readers / tablets, there may be multiple of each mode, depending on the content being displayed. Additionally, other modes may be included, such as Animation (also known as "A2 Mode"), and the display controller may be programmed to automatically switch between modes based on displayed content or user actions (eg, touch with a stylus).

[0012] As discussed in U.S. Pat. No. 11,686,989, in a multi-particle system using process black or process white, driving between the white and black states may require very different impulse potentials (voltage accumulated over time). For example, in ACeP®, which includes a negative white particle and three differently charged positive particles that together produce the black state, achieving a good black state may require a much larger impulse potential than a good white state. That is, to produce white, it is only necessary to place the negative white particle between the viewer and the colored particles, whereas to achieve a good black state, all the positively charged particles must be driven to the viewing surface and mixed, and all the white particles must be driven behind the positively charged colored particles. In a typical "GC" mode, the white and black states are achieved by DC balancing so that the round trip between the black and white states does not produce an impulse potential for these color states. However, this comes at the expense of a longer waveform, i.e., typically about 1 second, e.g., between 500ms and 3 seconds, e.g., between 700ms and 1 second. For DU mode, the desired switching time between the black and white states needs to be much shorter, e.g., less than 500 milliseconds, e.g., less than 300 milliseconds, e.g., about 250 milliseconds. However, because there is a difference in impulse potential between the black and white states, the impulse potential must be carefully managed to prevent charge accumulation on the pixel, resulting in a poor color state at a later time. This situation may be encountered in an e-reader, where the reader reads 20 pages of text and then sees a full color image.

[0013] The term "gray state" is used herein in its conventional sense in the field of imaging to refer to a state between two extreme optical states of a pixel, and does not necessarily imply a black-to-white transition between the two extreme states. For example, several of the Iink patents and published applications referenced below describe electrophoretic displays in which the extreme states are white and dark blue, such that the intermediate "gray state" is actually a light blue. In fact, as previously discussed, the change in optical state may not be a change in color at all. The terms "black" and "white" may be used hereinafter to refer to the two extreme optical states of a display, and should be understood to generally include extreme optical states that are not strictly black and white, such as the white and dark blue states described above.

[0014] The terms "bistable" and "bistable" are used herein in their conventional sense in the art to refer to a display including display elements having first and second display states that differ in at least one optical property, and such that after any given element is driven to assume its first or second display state by means of an addressing pulse of finite duration, that state will persist after termination of the addressing pulse for at least several times (e.g., at least four times) the shortest addressing pulse duration required to change the state of the display element. Some particle-based electrophoretic displays capable of supporting grayscale are shown in U.S. Patent No. 77170670 to be stable not only in their extreme black and white states, but also in their intermediate grayscale states, and so are some other types of electro-optical displays. This type of display is correctly referred to as "multistable" rather than bistable, although for convenience, the term "bistable" may be used herein to cover both bistable and multistable displays.

[0015] The term "impulse", when used in reference to driving an electrophoretic display, refers to the integral of the applied voltage with respect to time during which the display is driven.

[0016] Particles that absorb, scatter or reflect light of a broad band or selected wavelength are referred to herein as colored or pigment particles. Various materials that absorb or reflect light other than pigments (strictly speaking, the term refers to insoluble colored materials), such as dyes or photonic crystals, can also be used in the electrophoretic media and displays of the present invention.

[0017] Particle-based electrophoretic displays have been the subject of intensive research and development for many years. In such displays, multiple charged particles (sometimes called pigment particles) are moved in a fluid under the influence of an electric field. Compared to liquid crystal displays, electrophoretic displays can have the properties of good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, long-term image quality issues with these displays have prevented their widespread use. For example, the particles that make up electrophoretic displays tend to settle easily, resulting in insufficient lifetimes for these displays.

[0018] As mentioned above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, the fluid is a liquid, but a gaseous fluid can be used to produce an electrophoretic medium; 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. Patent Nos. 7,321,459 and 7,236,291. When such a gas-based electrophoretic medium is used in a direction that allows particle sedimentation, such as in a sign where the medium is located in a vertical plane, such a medium appears to be susceptible to the same type of particle sedimentation problems as liquid-based electrophoretic media. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoretic media than in liquid-based electrophoretic media because the viscosity of the gaseous suspension fluid is lower than that of the liquid suspension fluid, allowing the electrophoretic particles to settle more quickly.

[0019] Numerous patents and applications assigned to or under the names of the Massachusetts Institute of Technology (MIT) and Ink Corp. describe various techniques used in encapsulating electrophoretic and other electro-optical media. Such encapsulated media contain a number of small capsules, each of which itself contains an internal phase containing electrophoretically mobile particles in a fluid medium and a capsule wall surrounding the internal phase. Typically, the capsules themselves are held in a polymer binder to form an adhesive layer located between two electrodes. The techniques described in these patents and applications include:

[0020] (a) electrophoretic particles, fluids and fluid additives; see, for example, U.S. Pat. Nos. 7,002,728 and 7,679,814;

[0021] (b) capsules, adhesives and encapsulation processes; see, e.g., U.S. Pat. Nos. 6,922,276 and 7,411,719;

[0022] (c) microcell structures, wall materials, and methods of forming microcells; see, for example, U.S. Pat. Nos. 7,072,095 and 9,279,906;

[0023] (d) Methods for filling and sealing microlocations; see, e.g., U.S. Pat. Nos. 7,144,942 and 7,715,088;

[0024] (e) Films and subassemblies containing electro-optical materials; see, e.g., U.S. Pat. Nos. 6,982,178 and 7,839,564;

[0025] (f) Backplanes, adhesive layers and other auxiliary layers and methods used in displays; see, e.g., U.S. Patent Nos. 7,116,318 and 7,535,624;

[0026] (g) Color formation Color adjustment; see, e.g., U.S. Patent Nos. 6017584; 6545797; 6664944; 6788452; 6864875; 6914714; 6972893; 7038656; 7038670; 7046228; 7052571; 7075502; 7167155; 7385751; 7492505; 766768 4; 7684108; 7791789; 7800813; 7821702; 7839564; 7910175; 7952790; 7956841; 7982941; 8040594; 8054526; 8098418; 8159636; 8213076; 8363299; 8422116; 8441714; 8441716; 846 6852;8503063;8576470;8576475;8593721;8605354;8649084;8670174;8704756;8717664;8786935;8797634;8810899;8830559;8873129;8902153;8902491;8917439;8964282; 9013783; 9116412; 9146439; 9164207; 9170467; 9170468; 9182646; 9195111; 9199441; 9268191; 9285649; 9293511; 9341916; 9360733; 9361836; 9383623; and 9423666; and U.S. Patent Application Publication No. 2008 / 0043318; 2008 / 0048970; 2009 / 0225398; 2010 / 0156780; 2011 / 0043543; 2012 / 0326957; 2013 / 0242378; 2013 / 0278995; 2014 / 0055840; 2014 / 0078576; 2014 / 0340430; 2014 / 0340736; 2014 / 0362213; 2 015 / 0103394; 2015 / 0118390; 2015 / 0124345; 2015 / 0198858; 2015 / 0234250; 2015 / 0268531; 2015 / 0301246; 2016 / 0011484; 2016 / 0026062; 2016 / 0048054; 2016 / 0116816; 2016 / 0116818; and 2016 / 0140909;

[0027] (h) Methods for driving displays; see, e.g., U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,847; 7,242,514; 7,259,744; 7,304,787; 7312794; 7327511; 7408699; 7453445; 7492339; 7528822; 7545358; 7583251; 7602374; 7612760; 7679599; 7679813; 7683606; 7688297; 7729039; 7733311; 7733335; 7787169; 7859742; 7952557; 7956841; 7982479; 7999787; 8077141; 8125501; 81 39050; 8174490; 8243013; 8274472; 8289250; 8300006; 8305341; 8314784; 8373649; 8384658; 8456414; 8462102; 8514168; 8537105; 8558783; 8558785; 8558786; 8558855; 8576164; 8576259; 8593396; 8605032; 8643595; 8665206; 8681191; 8730 153; 8810525; 8928562; 8928641; 8976444; 9013394; 9019197; 9019198; 9019318; 9082352; 9171508; 9218773; 9224338; 9224342; 9224344; 9230492; 9251736; 9262973; 9269311; 9299294; 9373289; 9390066; 9390661; and 9412314; and U.S. Patent Application Publication No.2003 / 0102858; 2004 / 0246562; 2005 / 0253777; 2007 / 0091418; 2007 / 0103427; 2007 / 0176912; 2008 / 0024429; 2008 / 0024482; 2008 / 0136774; 2008 / 0291129; 2008 / 0303780; 2009 / 0174651; 2009 / 0195568; 2009 / 0322721; 2010 / 0194733; 2010 / 0194789; 2010 / 0220121; 2010 / 0265561; 2010 / 0283804; 2011 / 0063314; 2011 / 0175875; 2011 / 0193840; 2011 / 0193841; 2011 / 0199671; 2011 / 0221740; 2012 / 0001957; 2012 / 0098740; 2013 / 0063333; 2013 / 0194 250; 2013 / 0249782; 2013 / 0321278; 2014 / 0009817; 2014 / 0085355; 2014 / 0204012; 2014 / 0218277; 2014 / 0240210; 2014 / 0240373; 2014 / 0253425; 2014 / 0292830; 2014 / 0293398; 2014 / 0333685; 2014 / 0340734; 2015 / 0070744; 2 015 / 0097877; 2015 / 0109283; 2015 / 0213749; 2015 / 0213765; 2015 / 0221257; 2015 / 0262255; 2015 / 0262551; 2016 / 0071465; 2016 / 0078820; 2016 / 0093253; 2016 / 0140910; and 2016 / 0180777 (these patents and patent applications may be referred to hereinafter as MEDEOD (Methods for Driving Electro-optic Displays) applications);.

[0028] (i) Display applications; see, e.g., U.S. Patent Nos. 7,312,784 and 8,009,348; and

[0029] (j) Non-electrophoretic displays, such as those described in U.S. Patent No. 6,241,921; and U.S. Patent Application Publication No. 2015 / 0277160; and U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0030] Many of the above patents and applications recognize that the walls around discrete microcapsules in encapsulated electrophoretic media can be replaced by a continuous phase, thereby producing a so-called polymer dispersed electrophoretic display, wherein the electrophoretic medium includes a plurality of discrete electrophoretic fluid droplets and a continuous phase of polymer material, and the discrete electrophoretic fluid droplets within such polymer dispersed electrophoretic displays can be considered capsules or microcapsules, even though there is no discrete capsule membrane associated with each individual droplet; see, e.g., U.S. Patent No. 6,866,760. Therefore, for purposes of this application, such polymer dispersed electrophoretic media are considered a subclass of encapsulated electrophoretic media.

[0031] A related type of electrophoretic display is the so-called microcell electrophoretic display. In a microcell electrophoretic display, the charged particles and fluid are not encapsulated in microcapsules, but are retained in a plurality of cavities formed in a carrier medium (usually a polymer film). See, for example, U.S. Patent Nos. 6,672,921 and 6,788,449.

[0032] Although electrophoretic media are typically opaque (because, 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 operated in a so-called shutter mode, in which one display state is substantially opaque and one display state is light-transmissive. See, for example, U.S. Patents 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 on changes in electric field strength, can be operated in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optical displays can also be operated in a shutter mode. Electro-optical media operated in a shutter mode can be used in a multilayer structure for a full-color display; in such a structure, at least one layer adjacent to a viewing surface of the display is operated in a shutter mode to expose or hide a second layer that is farther from the viewing surface.

[0033] Encapsulated electrophoretic displays generally do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic devices, and offer further advantages, such as the ability to print or coat the display on a variety of flexible and rigid substrates (the use of the term "printing" is intended to include all forms of printing and coating, including but not limited to: predetermined amount coating, such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roller coating, such as doctor blade roller coating, forward and reverse roller coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing process; electrostatic printing process; thermal printing process; inkjet printing process; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar technologies). Thus, the resulting display can be flexible. In addition, because the display medium can be printed (using a variety of methods), the display itself can be manufactured inexpensively.

[0034] As described above, most simple prior art electrophoretic media display essentially only two colors. Such electrophoretic media either use a single type of electrophoretic particles having a first color in a colored fluid having a second, different color (in which case the first color is displayed when the particles are located near the viewing surface of the display, and the second color is displayed when the particles are spaced from the viewing surface), or use first and second types of electrophoretic particles having different first and second colors in a colorless fluid (in which case the first color is displayed when the first type of particles are located near the viewing surface of the display, and the second color is displayed when the second type of particles are located near the viewing surface). Typically, the two colors are black and white. If a full color display is desired, a color filter array can be placed on the viewing surface of a monochrome (black and white) display. Displays with color filter arrays rely on area sharing and color mixing to produce color stimulation. The available display area is shared by three or four primary colors (such as red / green / blue (RGB) or red / green / blue / white (RGBW), and the filters can be arranged in a one-dimensional (striped) or two-dimensional (2x2) repeating pattern. Other choices of primary colors or more than three primary colors are also known in the art. The three (in the case of an RGB display) or four (in the case of an RGBW display) sub-pixels are chosen to be small enough that at the expected viewing distance they visually blend together to form a single pixel with uniform color stimulation ("color mixing"). An inherent disadvantage of area sharing is that the colorant is always present and the color can only be modulated by switching the corresponding pixel of the underlying monochrome display to white or black (turning the corresponding primary color on or off). For example, in an ideal RGBW display, the red, green, blue and white primaries each occupy a quarter of the display area. Area sharing reduces the brightness and saturation of colors by switching colored pixels to black. Area sharing is particularly problematic when mixing yellow, because yellow is lighter than any other color of equal brightness, while saturated yellow is almost as bright as white. Switching blue pixels (one quarter of the display area) to black makes yellow too dark.

[0035] U.S. Patent Nos. 8,576,476 and 8,797,634 describe multicolor electrophoretic displays having a single backplane including independently addressable pixel electrodes and a common light-transmitting front electrode. Multiple electrophoretic layers are disposed between the backplane and the front electrode. The displays described in these applications are capable of rendering any primary color (red, green, blue, cyan, magenta, yellow, white, and black) at any pixel location. However, there are disadvantages to using multiple electrophoretic layers located between a single set of addressing electrodes. The electric field experienced by particles in a particular layer is lower than that of a single electrophoretic layer addressed with the same voltage. In addition, optical losses in the electrophoretic layer closest to the viewing surface (e.g., caused by light scattering or unwanted absorption) may affect the appearance of the image formed in the electrophoretic layer below.

[0036] A second form of electrophoretic medium capable of presenting any color at any pixel location is described in U.S. Patent No. 9,921,451. In the 451 patent, the electrophoretic medium includes four particles: white, cyan, magenta, and yellow, two of which are positively charged and two of which are negatively charged. However, the display of the 451 patent also suffers from the problem of color mixing in the white state. Because one of the particles has the same charge as the white particles, when the white state is desired, a certain amount of the particles with the same charge will move toward the viewing surface along with the white particles. Although complex waveforms can be used to overcome this unwanted hue, such waveforms will greatly increase the update time of the display and, in some instances, will cause unacceptable "flicker" between images.

[0037] As discussed above, with respect to U.S. Patent 11686989, one solution is to use an electrophoretic medium comprising four particles of white, cyan, magenta and yellow, wherein three of the particles are positively charged and the negatively charged particle is white. While all non-white particles are oppositely charged to the white particles, helping to reduce color contamination in the white state, this combination results in an unbalanced waveform when transitioning from a color state to a white or black state. In particular, the black state typically requires a continuous high positive drive to ensure that all positively charged particles are moved to the viewing surface. Summary of the invention

[0038] In a first aspect of the present invention, a method for driving an electrophoretic display having a plurality of pixels, each pixel being capable of displaying at least three optical states, including white, black, and a color that is neither white nor black. The method comprises driving the electrophoretic display with a first driving mode that allows transitions between all optical states; driving the electrophoretic display with a second driving mode that includes only transitions between black and white optical states, wherein in the second driving mode, the impulse potential experienced by the pixel when it changes from the white state to the black state is equal in magnitude and opposite in sign to the impulse potential experienced by the pixel when it changes from the black state to the white state; driving the electrophoretic display with a first transition mode, the first transition mode allowing transitions from the color state of the first driving mode to the white state or the black state of the second driving mode, wherein the first transition mode compensates for the excess impulse potential to be delivered to the pixel in the second driving mode; and driving the electrophoretic display with a second transition mode, the second transition mode allowing transitions from the white state or the black state of the second driving mode to the color state of the first driving mode, wherein the second transition mode compensates for the excess impulse potential that has been delivered to the pixel in the second driving mode. In one embodiment, in the first driving mode, the impulse potential experienced by the pixel from the white state to the black state is different in magnitude and opposite in sign from the impulse potential experienced by the pixel from the black state to the white state. In one embodiment, the first transition mode and the second transition mode do not have the same impulse potential compensation between the color state of the first driving mode and the white state of the second driving mode and between the color state of the first driving mode and the black state of the second driving mode. In one embodiment, the first transition mode and the second transition mode do not have the same waveform between the color state of the first driving mode and the white state of the second driving mode and between the color state of the first driving mode and the black state of the second driving mode. In one embodiment, in the second driving state, the waveform causing the transition from the white state to the black state includes at least five frames of maximum positive voltage. In one embodiment, in the second driving state, the waveform causing the transition from the black state to the white state includes at least five frames of maximum negative voltage. In one embodiment, the first driving mode is DC balanced. In one embodiment, the first transition mode and the second transition mode are not DC balanced. In one embodiment, each pixel can display at least eight optical states, and the first transition mode allows each of the six non-black and non-white color optical states to transition to the white state or black state of the second driving mode. In one embodiment, the eight optical states are black, white, red, magenta, yellow, green, cyan, and blue.

[0039] In another aspect, a display controller is configured to perform any of the above methods.

[0040] In another aspect, an electrophoretic display configured to implement any of the above methods. In one embodiment, the electrophoretic display includes an electrophoretic medium, the electrophoretic medium including at least three particles having different electrophoretic mobilities. In one embodiment, at least two of the three particles have the same charge, but different amounts of charge. In one embodiment, one of the particles is negatively charged and appears white. In one embodiment, the display includes three types of positively charged particles, each of which is partially light absorbing and has a different color than the other types of positively charged particles. In one embodiment, the electrophoretic medium is confined within a plurality of capsules or a plurality of microcells. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic cross-sectional view showing the positions of various colored particles in the electrophoretic medium of the present invention when displaying black, white, three subtractive primary colors and three additive primary colors.

[0042] Figure 2A is a generalized schematic diagram of an electrophoretic display with four types of particles in a non-polar fluid, where a full range of colors can be obtained on each pixel electrode. It is understood that in some embodiments, one negatively charged particle is white, one positively charged particle is yellow, one positively charged particle is magenta, and one positively charged particle is cyan, however, the present invention is not limited to the exemplary set of colors or combinations of charge polarity and magnitude.

[0043] Figure 2B The transition between a first optical state, with all particles of a first charge polarity at the viewing surface, and a second optical state, with particles of a second (opposite) polarity at the viewing surface, is shown.

[0044] Figure 2C The transition between a first optical state with all first charge polarity particles at the viewing surface and a third optical state with second (opposite) polarity particles behind the first polarity intermediately charged particles at the viewing surface is shown.

[0045] Figure 2D The transition between a first optical state with all first charge polarity particles at the viewing surface and a fourth optical state with second (opposite) polarity particles behind the first polarity less charged particles at the viewing surface is shown.

[0046] Figure 2EA transition between a first optical state, where the first optical state has all particles of a first charge polarity at the viewing surface, and a fifth optical state, where particles of the second (opposite) polarity are behind a combination of low and medium charged particles of the first polarity located at the viewing surface, is shown.

[0047] Figure 3 An exemplary equivalent circuit of a single pixel of an electrophoretic display is shown.

[0048] Figure 4 The layers of an exemplary electrophoretic color display are shown.

[0049] Figure 5 An exemplary push-pull drive scheme for addressing an electrophoretic medium comprising three subtractive color particles and one scattering (white) particle is shown. Such address pulses are typically accompanied by DC balancing clear pulses to enable each color state to switch to the other various color states.

[0050] Figure 6 The workflow of the drive modes that can be performed by the display controller using the method of the present invention is shown. In particular, the drive mode of the display changes according to the color content of the image to be displayed and / or the need for fast page turning and / or the need for stylus updating. In some embodiments, the controller automatically switches between modes. In other embodiments, switching modes requires user input.

[0051] Figure 7 is a summary diagram of the present invention showing the DUin and DUout transition patterns that compensate for impulse potentials when moving back and forth between "Global Complete" ("GC") mode and DU mode.

[0052] Figure 8 Waveforms that can be used to provide fast transitions between white and black optical states in direct update ("DU") mode are shown. Other waveforms can also be used as long as they produce offsetting impulse potentials when transitioning between black and white states.

[0053] Fig. 9A A series of waveform voltage frames for multiple transitions in the DUin mode (a mode of the present invention) are shown, which realizes the impulse potential compensation transition between the GC mode and the DU mode. It is worth noting that "duK" and "duW" correspond to the black and white optical states in the DU mode, respectively. K, W, GC2 and GC3 correspond to the black, white, generalized second color and third color in the GC mode, respectively. Typically, in the GC mode, K is the first color and W is the last color.

[0054] Fig. 9B shows the actual visual transition per frame in DUin mode, corresponding to Fig. 9A The waveform shown.

[0055] Fig. 10A A series of waveforms as voltage frames for multiple transitions in DUout mode are shown, which implement impulse potential compensation transitions between DU mode and GC mode.

[0056] Fig. 10B The actual visual transition of each frame in DUout mode is shown, which corresponds to Fig. 10A The waveform shown.

[0057] Fig.11 is a graphical example of how to compensate for impulse potential when switching between GC mode and DU mode. It is worth noting that the impulse compensation from GC to DU (i.e., DUin) is different from the impulse compensation from DU to GC (i.e., DUout). DETAILED DESCRIPTION

[0058] The present invention provides a method of driving a multi-pixel electrophoretic display designed to display at least three colors, such as eight, on each pixel. The method uses a first drive scheme that enables transitions between all colors that can be displayed on each pixel and a second drive scheme that only includes transitions that end in white or black, which is very useful for drawing black lines on a white page, reading black text on a white page, or reading white text on a black page. The second drive scheme is intended to allow the display to respond quickly to user input, such as a user "writing" with a stylus on a display that includes a touch screen or electromagnetic resonance (EMR) or another form of stylus or touch interaction. The present invention further provides a transition drive scheme for switching between the first drive scheme and the second drive scheme.

[0059] The present invention includes an improved four-particle electrophoretic medium including a first particle of a first polarity and three other particles of opposite polarity but with different charge amounts. Typically, such a system includes negatively charged white particles and positively charged particles of subtractive primary colors of yellow, magenta, and cyan. In addition, some particles can be designed so that their electrophoretic mobility is nonlinearly related to the strength of the applied electric field. Thus, when a high electric field (e.g., 20V or higher) of the correct polarity is applied, the electrophoretic mobility of one or more particles will experience a decrease. A schematic diagram of such a four-particle system is shown in FIG. Figure 1 as shown, and it can provide white, yellow, red, magenta, blue, cyan, green and black on each pixel.

[0060] like Figure 1As shown, each of the eight primary colors (red, green, blue, cyan, magenta, yellow, black, and white) corresponds to a different arrangement of four particles so that the viewer can see only those colored particles that are located on the viewing side of the white particles (i.e., the only particles that can scatter light). To achieve multiple colors, additional voltage levels must be used to more finely control the particles. In the concept described, the first particle (usually negatively charged) is reflective (usually white), while the other three oppositely charged particles (usually positively charged) include three substantially non-light-scattering ("SNLS") particles. The use of SNLS particles allows a variety of colors to be mixed and provides more color results than can be achieved using the same number of scattering particles. These thresholds must be sufficiently separated to avoid crosstalk, and this separation necessitates the use of high addressing voltages for certain colors. The disclosed four-particle electrophoretic medium can also be updated faster, requiring "less flickering" transitions, and produces a color spectrum that is more pleasing to the viewer (and therefore, more commercially valuable). Furthermore, the disclosed concept provides fast updates between black and white pixels (eg, less than 500 milliseconds, eg, less than 300 milliseconds, eg, less than 200 milliseconds, eg, less than 100 milliseconds), thereby enabling fast page turning of black text on a white background.

[0061] exist Figure 1 In the above, it is assumed that the viewing surface of the display is located at the top (as shown in the figure), that is, the user views the display from this direction and the light is incident from this direction. As mentioned above, in a preferred embodiment, only one of the four particles used in the electrophoretic medium of the present invention substantially scatters light, and Figure 1 In this case, the particles are assumed to be white pigments. The light-scattering white particles form white reflectors, through which the light is reflected by the white particles (such as Figure 1 Any particles above the white particles (shown) are viewed. Light entering the display viewing surface passes through these particles, reflects off the white particles, passes through these particles again, and exits the display. Therefore, the particles above the white particles absorb a variety of colors, and the color presented to the user is the color produced by the combination of particles above the white particles. Any particles below the white particles (behind them from the user's perspective) are obscured by the white particles and do not affect the displayed color. Since the second, third, and fourth particles do not scatter light substantially, their order or arrangement relative to each other is not important, but their order or arrangement relative to the white (light-scattering) particles is important for the reasons already explained.

[0062] More specifically, when the cyan, magenta, and yellow particles are below the white particle ( Figure 1In the case [A]), there is no particle above the white particle, and the pixel only displays white. When a particle is above a white particle, the color of that particle is displayed. Figure 1 In the cases [B], [D], and [F], the colors are yellow, magenta, and cyan, respectively. When two particles are located above a white particle, the color displayed is a combination of the colors of the two particles; Figure 1 In case [C], the magenta and yellow particles appear red, in case [E], the cyan and magenta particles appear blue, and in case [G], the yellow and cyan particles appear green. Finally, when all three colored particles are located above the white particle ( Figure 1 In the case [H]), all incoming light is absorbed by the three subtractive primary color particles and the pixel appears black.

[0063] One of the subtractive primary colors might be represented by a particle that scatters light, so the display would include two types of light-scattering particles, one of which is white and the other of which is colored. In this case, however, the position of the colored particles that scatter light relative to the other colored particles overlying the white particles is very important. For example, when representing black (when all three colored particles are located above the white particles), the scattering colored particles cannot be located above the non-scattering colored particles (otherwise these non-scattering particles would be partially or completely hidden behind the scattering particles, and the rendered color would be the color of the scattering colored particles, not black).

[0064] Figure 1 An idealized situation is shown in which the color is not contaminated (i.e., the light scattering white particles completely mask any particles located behind the white particles). In practice, masking of the white particles may not be perfect, so particles that are completely masked in the ideal situation may have a small amount of light absorption. This contamination generally reduces the brightness and chromaticity of the rendered color. In the electrophoretic media of the present invention, such color contamination should be minimized so that the resulting color meets industry standards for color rendering. A particularly supported standard is the standard for newspaper advertising production (SNAP), which specifies the L*, a*, and b* values ​​for each of the eight primary colors described above. (Hereinafter, "primary color" is used to refer to Figure 1 The eight colors shown, black, white, the three subtractive primaries, and the three additive primaries).

[0065] Figure 2A-2ESchematic cross-sections of four particle types used in the present invention are shown. A display layer utilizing an improved electrophoretic medium includes a first (viewing) surface 13 located on the viewing side and a second surface 14 located on the opposite side of the first surface 13. The electrophoretic medium is located between the two surfaces. Each space between two dashed vertical lines represents a pixel. Within each pixel, the electrophoretic medium can be addressed, and the viewing surface 13 of each pixel can be implemented Figure 1 The color states shown are achieved without the need for additional layers and without the need for a color filter array.

[0066] According to the standard of electrophoretic display, the first surface 13 includes a common electrode 11, which is light-transmissive, for example, constructed from a PET sheet with indium tin oxide (ITO) arranged thereon. On the second surface (14) there is an electrode layer 12, which includes a plurality of pixel electrodes 15. Such pixel electrodes are described in U.S. Patent No. 7,046,228, the entire contents of which are incorporated herein by reference. It should be noted that although it is mentioned that the pixel electrode layer is driven by an active matrix with a thin film transistor (TFT) backplane, the scope of the present invention includes other types of electrode addressing as long as these electrodes can achieve the desired function. For example, the top and bottom electrodes can be continuous. In addition, pixel electrode backplanes different from those described in Patent No. 7,046,228 are also applicable, and can include active matrix backplanes that can provide higher driving voltages than amorphous silicon thin film transistor backplanes.

[0067] Newly developed active matrix backplanes may include thin film transistors that include metal oxide materials such as tungsten oxide, tin oxide, indium oxide, zinc oxide, or more complex metal oxides such as indium gallium zirconium oxide. In these applications, each transistor using such metal oxide materials forms a channel forming region that allows faster switching of higher voltages. Such metal oxide transistors also allow thin film transistors (TFTs) to have less leakage in the "off" state than, for example, amorphous silicon TFTs. In a typical scanning TFT backplane comprising n rows, the time the transistor is in the "off" state is about (n-1) / n of the time required to refresh each row of the display. Any charge leakage from the storage capacitor associated with each pixel causes the electro-optical performance of the display to degrade. The TFT typically includes a gate electrode, a gate insulating film (usually SiO2), a metal source electrode, a metal drain electrode, and a metal oxide semiconductor thin film overlying the gate insulating film and at least partially overlapping the gate, source and drain electrodes. Such backplanes are available from manufacturers such as Sharp / Foxconn, Hyundai, and BOE. Such a backplane can provide a driving voltage of ±30V (or higher). In some embodiments, an intermediate voltage driver is also included, so the generated driving waveform may include five levels, or seven levels, or nine levels or more.

[0068] A preferred metal oxide material for such applications is indium gallium zinc oxide (IGZO). The electron mobility of IGZO-TFTs is 20-50 times that of amorphous silicon. By using IGZO TFTs in an active matrix backplane, it is possible to provide voltages greater than 30V via a suitable display driver. In addition, a source driver capable of supplying at least five levels (preferably seven levels) can provide different drive modes for a four-particle electrophoretic display system. In one embodiment, there will be two positive voltages, two negative voltages, and zero voltage. In another embodiment, there will be three positive voltages, three negative voltages, and zero voltage. In one embodiment, there will be four positive voltages, four negative voltages, and zero voltage. These levels can be selected in the range of about -27V to +27V without being subject to the limitations imposed by the above-mentioned top plane switching.

[0069] like Figure 2A-2EAs shown, the electrophoretic medium of the present invention includes four types of electrophoretic particles in a non-polar fluid 17. The first type of particle (W-*; open circles) is negatively charged and can be surface treated so that the electrophoretic mobility of the first particle depends on the strength of the driving electric field (discussed in more detail below). In this example, the electrophoretic mobility of the particle actually decreases under the action of a stronger electric field, which is somewhat counterintuitive. The second type of particle (M++*; black circles) is positively charged and can also be surface treated (or intentionally left untreated) so that the electrophoretic mobility of the second particle depends on the strength of the driving electric field, or so that the second particle's aggregation separates more slowly than the aggregation of the third and fourth particles after being driven to one side of the cavity containing the particles when the direction of the electric field is reversed. The third particle (Y+; checkered circles) is positively charged, but has a smaller charge than the second particle. In addition, the third particle can be surface treated, but the treatment does not cause the electrophoretic mobility of the third particle to depend on the strength of the driving electric field. That is, the third type of particle can be surface treated, but this surface treatment does not lead to the above-mentioned decrease in electrophoretic mobility when the electric field increases. The fourth type of particle (C+++; gray circle) has the highest positive charge and has the same type of surface treatment as the third type of particle. Figure 2A As shown, the colors of the particles are nominally white, magenta, yellow, and cyan to produce Figure 1 However, the present invention is not limited to this particular color combination, nor is it limited to one reflective particle and three absorbing particles. For example, the system can include a black absorbing particle and three reflective particles of red, yellow, and blue with appropriately matched reflective spectra, and when all three reflective particles are mixed and can be viewed on the surface, a process white state will be produced.

[0070] In a preferred embodiment, the first particles (negatively charged) are white and scattering. The second particles (positively charged, medium charge) are magenta and absorptive. The third particles (positively charged, low charge) are yellow and absorptive. The fourth particles (positively charged, high charge) are cyan and absorptive. Table 1 below shows the diffuse reflectance of exemplary yellow, magenta, cyan and white particles that can be used in the electrophoretic medium of the present invention, as well as the ratio of the absorption coefficient to the scattering coefficient based on the Kubelka-Munk analysis of these materials dispersed in a poly(isobutylene) matrix.

[0071] Table 1. Diffuse reflectance of preferred yellow, magenta, cyan and white particles.

[0072]

[0073] The electrophoretic medium of the present invention may be in any of the above forms. Thus, the electrophoretic medium may be unencapsulated, encapsulated in discrete capsules surrounded by capsule walls, encapsulated in sealed microcells, or in the form of a polymer dispersion medium. Pigments are described in detail elsewhere, such as in U.S. Pat. Nos. 9,697,778 and 9,921,451. Briefly, white particles W1 are a silanol-functionalized light-scattering pigment (titanium dioxide) as described in U.S. Pat. No. 7,002,728, to which is attached a polymeric material comprising a monomer of lauryl methacrylate (LMA). White particles W2 are polymer-coated titanium dioxide produced substantially as described in Example 1 of U.S. Pat. No. 5,852,196, the polymer coating comprising lauryl methacrylate and 2,2,2-trifluoroethyl methacrylate in a ratio of approximately 99:1. Yellow particles Y1 are CI Pigment Yellow 180, as generally described in U.S. Pat. No. 9,697,778, without coating, dispersed by grinding in the presence of Solsperse 19000. Yellow particles Y2 are CI Pigment Yellow 155, as generally described in U.S. Pat. No. 9,697,778, uncoated, and dispersed by grinding in the presence of Solsperse 19000. Yellow particles Y3 are CI Pigment Yellow 139, as generally described in U.S. Pat. No. 9,697,778, uncoated, and dispersed by grinding in the presence of Solsperse 19000. Yellow particles Y4 are CI Pigment Yellow 139, as generally described in U.S. Pat. No. 9,921,451, Example 4, which is coated by dispersion polymerization, combining trifluoroethyl methacrylate, methyl methacrylate, and dimethylsiloxane-containing monomers. Magenta particles M1 are a positively charged magenta material (dimethylquinacridone, CI Pigment Red 122), as described in U.S. Pat. No. 9,697,778 and Example 5 in U.S. Pat. No. 9,921,451, coated using vinylbenzyl chloride and LMA.

[0074] Magenta particles M2 are a CI Pigment Red 122 coated by dispersion polymerization, methyl methacrylate, and dimethylsiloxane containing monomers as described in Example 6 of U.S. Patent No. 9,921,451. Cyan particles C1 are a copper phthalocyanine material (CI Pigment Blue 15:3) coated by dispersion polymerization in combination with methyl methacrylate and dimethylsiloxane containing monomers as described in Example 7 of U.S. Patent No. 9,921,451. In some embodiments, it has been found that the color gamut can be improved by using Ink JetYellow 4GC (Clariant) as the core yellow pigment in combination with a methyl methacrylate surface polymer. The zeta potential of the yellow pigment can be adjusted by adding 2,2,2-trifluoroethyl methacrylate (TFEM) monomer and methacrylate-terminated poly(dimethylsiloxane).

[0075] U.S. Pat. No. 9,697,778 discusses in detail electrophoretic medium additives and surface treatments for promoting different electrophoretic mobilities, and proposed interaction mechanisms between surface treatments and surrounding charge control agents and / or free polymers, the entire contents of which are incorporated herein by reference. In such electrophoretic media, one method of controlling the interaction between the various types of particles is to control the type, amount, and thickness of the polymer coating on the particles. For example, in order to control the particle properties so that the particle-particle interaction between the second type of particles and the third and fourth types of particles is less than the particle-particle interaction between, for example, the third type of particles and the fourth type of particles, the second type of particles can be treated with a polymer surface, while the third and fourth types of particles are either not treated with a polymer surface or treated with a polymer surface treatment whose mass coverage per unit area of ​​the particle surface is lower than that of the second type of particles. More generally, the Hamaker constant (which is a measure of the strength of the van der Waals interaction between two particles, the pairing potential is proportional to the Hamaker constant and inversely proportional to the sixth power of the distance between the two particles) and / or the interparticle spacing needs to be adjusted by judiciously selecting the polymer coatings on the three types of particles.

[0076] As discussed in U.S. Pat. No. 9,921,451, different types of polymers can include different types of polymer surface treatments. For example, when the closest approach distance of oppositely charged particles is maximized by steric barriers (usually polymers grafted or adsorbed to one or two particle surfaces), the Coulomb interaction may be weakened. The polymer shell can be a covalently bonded polymer made by a grafting process or chemical adsorption known in the art, or it can be physically adsorbed onto the particle surface. For example, the polymer can be a block copolymer containing insoluble and soluble fragments. Alternatively, the polymer shell can be dynamic because it is a loose network of free polymers from the electrophoretic medium, and in the presence of an electric field and a sufficient amount and type of charge control agent (CCA discussed below), the free polymers are compounded with the pigment particles. Therefore, depending on the intensity and polarity of the electric field, the particles can have more associated polymers, which causes the particles to interact differently with containers (e.g., microcapsules or microunits) and other particles. [The extent of the polymer shell can be conveniently assessed by thermal gravimetric analysis (TGA), a technique in which the temperature of a dried sample of the particles is raised and the mass loss from pyrolysis is measured as a function of temperature. Using TGA, the mass fraction of the polymer particles can be measured and this can be converted to volume fraction using the known densities of the core pigment and the polymer attached to it.] Cases may be found where the polymer coating is lost but the core pigment is retained (these cases depend on the exact core pigment particles used). Various polymer combinations can be described below with reference to Figure 2A-2E For example, in some embodiments, the particles (typically the first and / or second particles) may have a covalently attached polymer shell that interacts strongly with the container (e.g., microunit or microcapsule). At the same time, other particles with the same charge have no polymer coating or are complexed with free polymer in solution, so those particles have little interaction with the container. In other embodiments, the particles (typically the first and / or second particles) will not have a surface coating, making it easier for the particles to form a charge double layer and experience reduced electrophoretic mobility in the presence of a strong electric field.

[0077] The fluid 17 in which the four particles are dispersed is transparent and colorless. The fluid contains charged electrophoretic particles that move in the fluid under the influence of an electric field. The preferred suspending fluid has a low dielectric constant (about 2), a high volume resistivity (about 10 15Ohm.cm), low viscosity (less than 5mPas), low toxicity and environmental impact, low water solubility (less than 10 parts per million (ppm) if using traditional aqueous encapsulation methods; but note that this requirement can be relaxed for non-encapsulated or certain micro-cell displays), high boiling point (greater than about 90°C), and low refractive index (less than 1.5). The last requirement is due to the use of high-refractive-index scattering (usually white) pigments, whose scattering efficiency depends on the mismatch in refractive index between the particle and the fluid.

[0078] Organic solvents, such as saturated linear or branched hydrocarbons, silicone oils, halogenated organic solvents, and low molecular weight halogen-containing polymers are some useful fluids. The fluid may include a single component or a mixture of more than one component to adjust its chemical and physical properties. The fluid may also contain a reactant or solvent for the microencapsulation process (if used), such as an oil-soluble monomer.

[0079] The fluid preferably has a low viscosity and a dielectric constant between about 2 and about 30, preferably between about 2 and about 15, to achieve high particle mobility. Examples of suitable dielectric fluids include hydrocarbons such as Isopar®, decahydronaphthalene (DECALIN), 5-ethylidene-2-norbornene, fatty oils, paraffin oils, silicone oils, aromatic hydrocarbons such as toluene, xylene, phenoxyethane, dodecylbenzene or alkylnaphthalene, halogenated solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorotoluotrifluorotoluene, 3,4,5-trichlorotoluotrifluorotoluene, chloropentafluorobenzene, dichlorononane or pentachlorobenzene, and perfluorinated solvents such as FC-43, FC-70 or FC-5060 produced by 3M Company (St. Paul, Minnesota), low molecular weight halogen-containing polymers such as poly(perfluoropropylene oxide) from TCI America, Portland, Oregon, poly(chlorotrifluoroethylene) such as Halocarbon Oils from Halocarbon Product Corp., Riverside, New Jersey, perfluoropolyalkyl ethers such as Galden from Ausimont Corporation or Krytox from DuPont de Nemours and Company, Delaware. Oils and Greases K-Fluid series, polydimethylsiloxane-based silicone oil (DC-200) from Dow Corning.

[0080] The electrophoretic medium also typically includes one or more charge control agents (CCAs) and may include charge directors. CCAs and charge directors typically include low molecular weight surfactants, polymeric agents, or mixtures of one or more ingredients that function to stabilize or otherwise change the sign and / or magnitude of the charge on the electrophoretic particles. CCAs are typically molecules that include ionic or other polar groups, hereinafter referred to as head groups. At least one of the positive or negative ionic head groups is preferably attached to a non-polar chain (typically a hydrocarbon chain), hereinafter referred to as a tail group. It is believed that CCAs form reverse micelles in the internal phase, and it is the small amount of charged reverse micelles that is responsible for the conductivity of the very non-polar fluids typically used as electrophoretic fluids.

[0081] The addition of CCA provides the generation of reverse micelles, consisting of a highly polar core, whose size can vary from 1 nm to tens of nanometers (it can be spherical, cylindrical or other geometric shapes), surrounded by non-polar tail groups of CCA molecules. In the electrophoretic medium, three phases can usually be distinguished: solid particles with a surface, a highly polar phase distributed in the form of very small droplets (reverse micelles) and a continuous phase containing the fluid. When an electric field is applied, both the charged particles and the charged reverse micelles can move in the fluid, so there are two parallel electrical conduction paths through the fluid (which itself usually has a very small conductivity).

[0082] The polar core of the CCA is thought to affect the charge of the surface by adsorbing on it. In electrophoretic displays, this adsorption can be to the surface of the electrophoretic particles or to the inner walls of the microcapsules (or other solid phases, such as microcell walls) to form structures similar to reverse micelles, which are referred to as hemi-micelles in the following. When one ion of the ion pair is more strongly attached to the surface than the other ion (e.g., by covalent bonds), ion exchange between the hemi-micelle and the unbound reverse micelle can result in charge separation, where the more strongly bound ion remains associated with the particle, while the less strongly bound ion is incorporated into the core of the free reverse micelle.

[0083] It is also possible that the ionic material forming the CCA head group may induce ion pair formation on the particle (or other) surface. Thus, CCA may perform two basic functions: generating charge on the surface and separating charge from the surface. Charge generation may be due to acid-base or ion exchange reactions between some moiety present in the CCA molecule or otherwise incorporated into the reverse micelle core or some moiety of the fluid and the particle surface. Thus, useful CCA materials are those that are able to participate in such reactions or any other charging reactions known in the art.

[0084] Non-limiting categories of charge control agents used in the medium of the present invention include organic sulfates or sulfonates, metal soaps, block or combined copolymers, organic amides, organic zwitterions, and organic phosphates and phosphonates. Useful organic sulfates and sulfonates include, but are not limited to, sodium bis(2-ethylhexyl)sulfosuccinate, calcium dodecylbenzenesulfonate, calcium petroleum sulfonate, neutral or alkaline barium dinonylnaphthalenesulfonate, neutral or alkaline calcium dinonylnaphthalenesulfonate, sodium dodecylbenzenesulfonate, and ammonium lauryl sulfate. Useful metal soaps include, but are not limited to, alkaline or neutral barium carbolate, calcium carbolate, cobalt, calcium, copper, manganese, magnesium, nickel, zinc, aluminum, and iron carboxylates such as cyclohexane acid, octanoic acid, oleic acid, palmitic acid, stearic acid, and myristic acid. Useful block or combination copolymers include, but are not limited to: AB diblock copolymers of (A) 2-(N,N-dimethylamino)ethyl methacrylate quaternized with methyl p-toluenesulfonate and (B) poly(2-ethylhexyl methacrylate), and combination graft copolymers having a poly(12-hydroxystearic acid) oil-soluble tail and a molecular weight of about 1800, pendant from an oil-soluble anchoring group of poly(methyl methacrylate-methacrylic acid). Useful organic amides / amines include, but are not limited to, polyisobutylene succinimides such as OLOA 371 or 1200 (available from Chevron Oronite LLC, Houston, Texas), or SOLSPERSE 17000 or 19000 (available from Lubrizol, Wickliffe, Ohio: Solsperse is a registered trademark), and N-vinyl pyrrolidone polymers. Useful organic zwitterions include, but are not limited to, lecithin. Useful organic phosphates and phosphonates include, but are not limited to, sodium salts of phosphated mono- and di-glycerides with saturated and unsaturated acid substituents. Useful tail groups for CCA include olefin polymers, such as poly(isobutylene), with molecular weights ranging from 200 to 10,000. The head group may be a sulfonic acid, phosphoric acid or carboxylic acid or an amide, or an amino group, such as a primary, secondary, tertiary or quaternary ammonium group. A class of CCAs useful in the disclosed four-particle electrophoretic medium is disclosed in U.S. Patent Publication No. 2017 / 0097556, which is incorporated herein by reference in its entirety. Such CCAs typically include a quaternary amine head group and an unsaturated polymer tail, i.e., including at least one CC double bond. The polymer tail is typically a fatty acid tail. A variety of CCA molecular weights may be used. In some embodiments, the molecular weight of the CCA is 12,000 g / mol or greater, such as between 14,000 g / mol and 22,000 g / mol.

[0085] The charge adjuvant used in the medium of the present invention can shift the charge on the surface of the electrophoretic particles, as described in detail below. Such charge adjuvants can be Bronsted acids or Lewis acids or bases. Exemplary charge adjuvants are disclosed in U.S. Patent Nos. 9765,015, 10233339 and 10782586, all of which are incorporated herein by reference in their entirety. Exemplary adjuvants may include polyhydroxy compounds containing at least two hydroxyl groups, including but not limited to ethylene glycol, 2,4,7,9-tetramethyldecyne-4,7-diol, poly(propylene glycol), pentaethylene glycol, tripropylene glycol, triethylene glycol, glycerol, pentaerythritol, glycerol tri(12-hydroxystearate), glycerol monohydroxystearate and ethylene glycol monohydroxystearate. Examples of amino alcohol compounds containing at least one alcohol functional group and one amine functional group in the same molecule include, but are not limited to, triisopropanolamine, triethanolamine, ethanolamine, 3-amino-1-propanol, o-aminophenol, 5-amino-1-pentanol, and tetrakis(2-hydroxyethyl)ethylenediamine. In some embodiments, the charge adjuvant is present in the electrophoretic display medium in an amount of about 1 to about 500 milligrams per gram ("mg / g"), more preferably about 50 to about 200 mg / g.

[0086] Particle dispersion stabilizers may be added to prevent particle flocculation or attachment to the capsule or other walls or surfaces. For typical high resistivity liquids used as fluids in electrophoretic displays, non-aqueous surfactants may be used. These surfactants include, but are not limited to, glycol ethers, acetylene glycols, alkanolamides, sorbitol derivatives, alkylamines, quaternary amines, imidazoline compounds, dialkyl oxides, and sulfosuccinates.

[0087] As described in U.S. Pat. No. 7,170,670, the bistability of the electrophoretic medium can be improved by incorporating into the fluid a polymer having a number average molecular weight in excess of about 20,000 which does not substantially absorb the electrophoretic particles; poly(isobutylene) is a preferred polymer for this purpose. In addition, for example, as described in U.S. Pat. No. 6,693,620, particles with fixed surface charges form an oppositely charged double layer in the surrounding fluid. The ionic head groups of CCA can ionically pair with charged groups on the surface of the electrophoretic particles to form a layer of immobilized or partially immobilized charged material. Outside this layer is a diffusion layer comprising charged (reverse) micelles comprising CCA molecules in the fluid. In conventional DC electrophoresis, the application of an electric field produces a force on the fixed surface charges and an opposite force on the mobile countercharges, causing sliding within the diffusion layer and movement of the particles relative to the fluid. The potential on the sliding surface is called the zeta potential.

[0088] As a result, certain particle types in an electrophoretic medium have different electrophoretic mobilities, depending on the strength of the electric field across the electrophoretic medium. For example, when a first (low strength, i.e., about ±10 V or less) electric field is applied to the electrophoretic medium, a first type of particle moves in one direction relative to the electric field, however, when a second (high strength, i.e., about ±20 V or more) electric field is applied, which has the same polarity as the first field, the first type of particle begins to move in the opposite direction relative to the electric field. It is speculated that this behavior arises from the fact that conduction in highly nonpolar fluids is mediated by oppositely charged micelles or oppositely charged electrophoretic particles. Therefore, any electrochemically generated protons (or other ions) are likely to be transported in the nonpolar fluid in the micelle core or adsorbed on the electrophoretic particles. For example, as described in U.S. Pat. No. 9,697,778 Figure 5 As shown in Figure B, a positively charged reverse micelle may approach a negatively charged electrophoretic particle traveling in the opposite direction, where the reverse micelle is adsorbed into the electrical double layer surrounding the negatively charged particle. (The electrical double layer consists of a charge diffusion layer with enhanced counter-ion concentration and a semi-micelle surface adsorption coating on the particle; in the latter case, the reverse micelle charge is associated with the particle within a sliding envelope, which, as described above, defines the particle's zeta potential.) Through this mechanism, the electrochemical current of positively charged ions flows through the electrophoretic fluid, and negatively charged particles may be biased toward more positive charges. Therefore, the electrophoretic mobility of the first type of negatively charged particle, for example, is a function of the magnitude of the electrochemical current and the residence time of the positive charge close to the particle surface, which is a function of the electric field strength.

[0089] In addition, as described in U.S. Pat. No. 9,697,778, positively charged particles can also be prepared, which also exhibit different electrophoretic mobilities depending on the applied electric field. In some embodiments, secondary (or co-level) CCAs can be added to the electrophoretic medium to adjust the zeta potential of various particles. Careful selection of co-level CCAs can change the zeta potential of one particle while leaving the zeta potential of other particles essentially unchanged, allowing close control of the electrophoretic velocities of various particles and the interactions between particles during switching.

[0090] In some embodiments, a portion of the charge control agent used in the final formulation is added during the synthesis of the electrophoretic particles to design the desired zeta potential and influence the reduction in electrophoretic mobility caused by strong electric fields. For example, it has been observed that the addition of a quaternary amine charge control agent during the polymer grafting process results in a certain amount of CCA complexed with the particles. (This can be confirmed by removing the particles from the electrophoretic fluid and then stripping the material on the pigment surface with tetrahydrofuran (THF) to remove all adsorbed material. When the THF extract is evaluated by 1H NMR, it can be clearly seen that a large amount of CCA is adsorbed on the pigment particles or complexed with the surface polymer). Experiments have shown that high CCA content in the particle surface polymer helps to form a charge double layer around the particles under the action of strong electric fields. For example, magenta particles with a charge control agent (CCA) content of more than 200 mg per gram of finished magenta particles have excellent retention characteristics in high positive electric fields. (See, e.g. Figure 2C and as described above). In some embodiments, the CCA comprises a quaternary amine head group and a fatty acid tail group. In some embodiments, the fatty acid tail is unsaturated. When some particles in the electrophoretic medium contain a higher CCA loading, it is important to have particles with uniform electrophoretic mobility that do not contain a large amount of CCA loading, such as less than 50 mg of charge control agent (CCA) per gram of finished particles, such as less than 10 mg of charge control agent (CCA) per gram of finished particles.

[0091] In other embodiments, an electrophoretic medium comprising four particles in the presence of Solsperse 17000 in Isopar E benefits from the addition of a small amount of an acidic material, such as, for example, an aluminum salt of di-tert-butyl salicylic acid (Bontron E-88, available from Orient, Kenilworth, NJ). The addition of the acidic material causes the zeta potential of many, though not all, particles to become more positive. In one embodiment, about 1% of the acidic material and 99% of Solsperse 17000 (based on the combined weight of the two materials) shifts the zeta potential of the third type of particle (Y+) from -5 mV to about +20 mV. Whether a Lewis acidic material, such as an aluminum salt, changes the zeta potential of a particular particle will depend on the specifics of the particle surface chemistry.

[0092] Table 2 shows exemplary relative zeta potentials of three types of colored particles and a single white particle in a preferred embodiment.

[0093] Table 2. Relative zeta potential of colored particles in the presence of the relative zeta potential of white particles.

[0094]

[0095] In one embodiment, the zeta potential of the negative (white) particles is -30 mV, and the remaining three particles are all positive relative to the white particles. Thus, a display including positive cyan, magenta, and yellow particles can switch between a black state (all colored particles are in front of the white particles relative to the viewing surface) and a white state (the white particles are closest to the viewer and prevent the viewer from perceiving the remaining three particles). Conversely, when the zeta potential of the white particles is 0 V, the negatively charged yellow particles are the most negative of all the particles, so a display including them switches between yellow and blue states. This would also occur if the white particles were positively charged. However, the positively charged yellow particles would be more positively charged than the white particles unless their zeta potential exceeded +20 mV.

[0096] The behavior of the electrophoretic media of the present invention is consistent with the mobility of the white particles (expressed as zeta potential in Table 2) being dependent on the applied electric field. Thus, in the example shown in Table 2, when addressed using a low voltage, the white particles may behave as if their zeta potential is -30 mV, but when addressed using a higher voltage, the white particles may behave as if their zeta potential is more positive, perhaps even as high as +20 mV (matching the zeta potential of the yellow particles). Thus, when addressed using a low voltage, the display switches between black and white states, but when addressed using a higher voltage, the display switches between blue and yellow states.

[0097] Figure 2B-2E The movement of various particles under high (e.g., "±H", e.g., ±20V, e.g., ±25V) electric fields and low (e.g., "±L", e.g., ±5V, e.g., ±10V) electric fields is shown. For ease of explanation, each dotted box represents a pixel, which is surrounded by a top light-transmitting electrode 21 and a bottom electrode 22, which may be a pixel electrode of an active matrix, but may also be a light-transmitting electrode or a segmented electrode, etc. Figure 2B-2E As shown, starting from a first state, where all positively charged particles are present at the viewing surface (nominal black), the electrophoretic medium can be driven into four different optical states. In a preferred embodiment, a white optical state ( Figure 2B ), magenta optical state ( Figure 2C ), yellow optical state ( Figure 2D ) and the red optical state ( Figure 2E ). Obviously, Figure 1 The remaining four optical states in can be achieved by reversing the order of the initial state and the driving electric field, such as Figure 5 Briefly shown.

[0098] When using low voltage addressing, such as Figure 2BAs shown, for the case when a negative voltage is applied to the backplane, the behavior of the particles depends on their relative zeta potential, and their relative speed is shown by the arrows. Therefore, in this example, the cyan particles move faster than the magenta particles, and the magenta particles move faster than the yellow particles. The first (positive) pulse does not change the position of the particles because their movement is already restricted by the walls of the housing. The second (negative) pulse swaps the positions of the colored particles and the white particles, so the display switches between black and white states, although the instantaneous color reflects the relative mobility of the colored particles. Reversing the starting position and polarity of the pulse allows a transition from white to black. Therefore, compared to other black and white formulations that obtain multiple colors via process black or process white, this embodiment provides black and white updates that require lower voltages (and consume less power).

[0099] exist Figure 2C In the embodiment of the present invention, the first (positive) pulse has a high positive voltage, which is sufficient to reduce the mobility of the magenta particles (i.e., the particles with the middle mobility among the three positively charged colored particles). Due to the reduced mobility, the magenta particles are essentially frozen in place, and the subsequent low voltage pulse in the opposite direction causes the cyan, white, and yellow particles to move more than the magenta particles, thereby producing a magenta color at the viewing surface, with the negatively charged white particles behind the magenta particles. Importantly, if the starting position and polarity of the pulses are reversed (equivalent to viewing the display from the side opposite to the viewing surface, i.e., through electrode 22), then this pulse sequence will produce a green color (i.e., a mixture of yellow and cyan particles).

[0100] exist Figure 2D In the embodiment of the present invention, the first pulse is a low voltage, which does not significantly reduce the mobility of the magenta particles or the white particles. However, the second pulse is a high negative voltage, which reduces the mobility of the white particles. This allows a more efficient race between the three positively charged particles, allowing the slowest particle (yellow in this example) to remain visible in front of the white particles, whose movement has been weakened by the previous negative pulse. It is worth noting that the yellow particles do not reach the top surface of the cavity containing the particles. Importantly, if the starting position and polarity of the pulses are reversed (equivalent to viewing the display from the side opposite to the viewing surface, i.e., through electrode 22), this pulse sequence will produce a blue color (i.e., a mixture of magenta and cyan particles).

[0101] at last, Figure 2E It is shown that when both pulses are high voltage, the first high positive pulse reduces the mobility of the magenta particles, while the second high negative pulse reduces the mobility of the white particles, thereby enhancing the race between cyan and yellow. This produces the color red. Importantly, if the starting position and polarity of the pulses are reversed (equivalent to viewing the display from the side opposite to the viewing surface, i.e. through electrode 22), this pulse sequence will produce cyan.

[0102] In order to achieve a high resolution display, individual pixels of the display must be addressable without interference from adjacent pixels. One way to achieve this is to provide an array of non-linear elements, such as transistors or diodes, with at least one non-linear element associated with each pixel, thereby producing an "active matrix" display. An addressing or pixel electrode is connected to an appropriate voltage source through the associated non-linear element, thereby addressing a pixel. Typically, when the non-linear element is a transistor, the pixel electrode is connected to the drain of the transistor, and this arrangement will be assumed in the following description, although this is essentially arbitrary and the pixel electrode can be connected to the source of the transistor. Conventionally, in high resolution arrays, the pixels are arranged in a two-dimensional array of rows and columns, so that any particular pixel is uniquely defined by the intersection of a particular row and a particular column. The sources of all transistors in each column are connected to a single column electrode, and the gates of all transistors in each row are connected to a single row electrode; again, the assignment of sources to rows and gates to columns is conventional but essentially arbitrary and can be reversed if desired. The row electrodes are connected to a row driver which essentially ensures that only one row is selected at any given moment, i.e. a select voltage is applied to the selected row electrode to ensure that all transistors in the selected row are conductive, while a non-select voltage is applied to all other rows to ensure that all transistors in these non-selected rows are non-conductive. The column electrodes are connected to a column driver which applies a selected voltage to each column electrode to drive the pixels in the selected row to the desired optical state. (The above voltages are relative to a common front electrode which is usually located on the side of the electro-optic medium opposite the non-linear array and extends across the display). After a preselected interval known as the "row addressing time", the selected row is deselected, the next row is selected, and the voltage on the column driver is changed so that the next row of the display is written. This process is repeated to write the entire display row by row.

[0103] Typically, each pixel electrode has a capacitor electrode associated therewith, such that the pixel electrode and the capacitor electrode form a capacitor; see, for example, International Patent Application WO01 / 07961. In some embodiments, an N-type semiconductor (e.g., amorphous silicon) may be used to form the transistor, and the "select" and "non-select" voltages applied to the gate electrode may be positive and negative, respectively.

[0104] In the attached figure Figure 3An example equivalent circuit for a single pixel of an electrophoretic display is described. As shown, the circuit includes a capacitor 10 formed between a pixel electrode and a capacitor electrode. The electrophoretic medium 20 is represented as a capacitor and a resistor in parallel. In some instances, direct or indirect coupling capacitance 30 (commonly referred to as "parasitic capacitance") between the gate electrode of a transistor associated with a pixel and the pixel electrode may introduce unwanted noise into the display. Typically, parasitic capacitance 30 is much smaller than the parasitic capacitance of storage capacitor 10, and when a row of pixels of the display is selected or deselected, parasitic capacitance 30 may cause the pixel electrode to generate a small negative offset voltage, also known as a "snap-back voltage," which is typically less than 2 volts. In some embodiments, to compensate for the unwanted "snap-back voltage," a common potential V may be provided to the top plane electrode and the capacitor electrode associated with each pixel. com , so that when V com Set to equal the snap-back voltage (V KB ), each voltage supplied to the display is offset by the same amount and no net DC imbalance is experienced.

[0105] However, when V com Problems can arise when the voltage is set to a voltage that does not compensate for the snap-back voltage. This occurs when a higher voltage needs to be applied to the display than the backplane alone can provide. As is well known in the art, for example, if the backplane supply is selected to be nominally +V, 0, or -V, and for example V com If a negative voltage is required, V com The potential must be raised to at least zero. Therefore, a waveform used to address a display with positive and negative voltages using top plane switching must have a voltage distribution assigned to more than one V com Voltage settings for each of the specific frames.

[0106] A set of waveforms for driving a color electrophoretic display having four particles is described in U.S. Pat. No. 9,921,451, which is incorporated herein by reference. In U.S. Pat. No. 9,921,451, seven different voltages are applied to the pixel electrode: three positive voltages, three negative voltages, and zero voltage. However, in some embodiments, the maximum voltage used in these waveforms is higher than the voltage that the amorphous silicon thin film transistor can handle. In this example, a suitable high voltage can be obtained by using top plane switching. When (as described above) V com Deliberately set to V KB When using top plane switching, a separate power supply can be used. However, when using top plane switching, use comIt is costly and inconvenient to provide the same number of independent power supplies. In addition, top plane switching is known to increase bounce, thereby reducing the stability of the color state.

[0107] The electrophoretic fluid of the present invention can be used to construct a display device in several ways known in the prior art. The electrophoretic fluid can be encapsulated in a microcapsule, or incorporated into a microcell structure, which is then sealed with a polymer layer. The microcapsule or microcell layer can be coated or embossed on a plastic substrate or film, which has a transparent conductive material coating. The assembly can be laminated to a backplane with pixel electrodes using a conductive adhesive. Alternatively, the electrophoretic fluid can also be directly distributed on a thin open-cell grid, which has been arranged on a backplane including an active matrix of pixel electrodes. The filled grid can then be top-sealed with an integrated protective film / transparent electrode.

[0108] Figure 4 A schematic cross-sectional view (not to scale) of a display structure 200 suitable for use with the present invention is shown. In display 200, the electrophoretic fluid is illustrated as being confined in microcells, although an equivalent structure comprising microcapsules may also be used. Substrate 202 may be glass or plastic, on which are located pixel electrodes 204, which may be individual addressing segments or may be associated with thin film transistors in an active matrix arrangement. (The combination of substrate 202 and electrodes 204 is often referred to as the backplane of the display). Layer 206 is an optional dielectric layer applied to the backplane in accordance with the present invention. (Methods for depositing suitable dielectric layers are described in U.S. Patent Application No. 16 / 862,750, which is incorporated herein by reference). The front plane of the display includes a transparent substrate 222 on which is located a transparent conductive coating 220. Above electrode layer 220 is an optional dielectric layer 218. Layer (or layers) 216 is a polymer layer, which may include a base layer for adhering the microcell to transparent electrode layer 220, and some residual polymer comprising the bottom of the microcell. The walls of microcell 212 are used to contain the electrophoretic fluid 214. The microcells are sealed with layer 210, and the entire front planar structure is adhered to the backplane with a conductive adhesive layer 208. Processes for forming microcells are described in the prior art, such as U.S. Pat. No. 6,930,818. In some examples, the microcells are less than 20 microns deep, such as less than 15 microns deep, such as less than 12 microns deep, such as about 10 microns deep, such as about 8 microns deep.

[0109] Due to the availability of manufacturing equipment and the cost of various starting materials, most commercial electrophoretic displays use amorphous silicon based thin film transistors (TFTs) in the construction of the active matrix backplane (202 / 204). Unfortunately, amorphous silicon thin film transistors become unstable when the gate voltage provided allows switching of voltages above approximately + / -15V. Nevertheless, as described below, the performance of the ACeP is improved when the amplitude of the high positive and negative voltages is allowed to exceed + / -15V. Therefore, as previously disclosed, improved performance can be achieved by additionally changing the bias of the top light-transmitting electrode relative to the bias of the backplane pixel electrode (also known as top plane switching). Therefore, if a voltage of +30V (relative to the backplane) is required, the top plane can be switched to -15V while the corresponding backplane pixel is switched to +15V. For example, U.S. Patent No. 9,921,451 describes in more detail a method of driving a four-particle electrophoretic system using top plane switching.

[0110] These waveforms require that each pixel of the display can be driven at five different addressing voltages, namely +V high 、+V low , 0, -V low and -V high , shown in the figure are 30V, 15V, 0, -15V and -30V. In practical applications, you may tend to use more addressing voltages. If there are only three voltages (i.e. +V high , 0, and -V high ), you can use V high Voltage pulse addressing, but with a duty cycle of 1 / n, allows for parallelism with lower voltages (such as V high / n, where n is a positive integer greater than 1) to address the same result.

[0111] Figure 5 A typical waveform (in simplified form) for driving the four particle color electrophoretic display systems described above is shown. This waveform has a "push-pull" structure: that is, the waveform consists of two dipoles containing pulses of opposite polarity. The size and length of these pulses determine the color obtained. There should be at least five such voltage levels. Figure 5 High positive voltages, low positive and negative voltages, and zero voltage are shown. Typically, "Low" (L) refers to a range of about 5-15V, while "High" (H) refers to a range of about 15-30V. In general, the higher the magnitude of the "High" voltage, the better the color gamut achieved by the display. In some embodiments, an additional "Middle" (M) level is used, typically around 15V; however, the value of M depends somewhat on the composition of the particles and the environment of the electrophoretic medium. In many of the waveforms shown below, +V high / -V high = ±24V, +V med / -Vmed = ±17V, +V low / -V low = ±10V, which is achieved using a power management integrated circuit (PMIC) and a driving backplane containing metal oxide transistors (such as IGZO), as described above. Commercially available suitable controllers can be used for the display of the present invention, such as UltraChip UC8152c or UC8159c or Solomon Systech SPD1656.

[0112] Although Figure 5 The simplest dipoles required to form color are shown, but it will be appreciated that actual waveforms may be multiple repetitions of these patterns, or other patterns that are non-periodic and use more than five voltage levels. Typically such waveforms are shown as a series of impulses corresponding to a frame, i.e. the amount of time between when the gates of the active matrix array TFTs are turned on for a new cycle. Thus, Figures 9A-10B , for example, including the number of frames, where it is understood that each frame represents approximately 20 milliseconds. However, the size of each frame may be different, for example, due to a larger array or faster transistors.

[0113] Of course, using Figure 5 The drive pulses in the image are dependent upon the process of the particles starting from a known state, which is unlikely to be the last color displayed on the pixel. Therefore, the drive pulses are preceded by a series of reset pulses, which increase the time required for the pixel to update from the first color to the second color. Reset pulses are described in more detail in U.S. Patent No. 10,593,272, which is incorporated herein by reference. The lengths of these pulses (refresh and address) and any rests (i.e., zero voltage periods between them) can be selected so that the entire waveform (i.e., the integral of the voltage over time over the entire waveform) is DC balanced (i.e., the integral of the voltage over time is essentially zero). DC balance can be achieved by adjusting the lengths of the pulses and rests in the reset phase so that the net impulse provided by the reset phase is equal in magnitude and opposite in sign to the net impulse provided by the addressing phase, during which the display is switched to a particular desired color. However, if Figure 2B-2E As shown, the starting state of the eight primary colors is either black or white, which can be achieved by a continuous low voltage drive pulse. The ease of achieving this starting state further reduces the update time between states, which is more pleasant for the user and also reduces power consumption (thus extending battery life).

[0114] Furthermore, the above discussion of waveforms, especially the DC balance, ignores the issue of snapback voltage. In reality, as mentioned earlier, each backplane voltage will be offset from the voltage provided by the power supply by an amount equal to the snapback voltage V KB Therefore, if the power supply used provides +V, 0, and -V, the backplane will actually receive V+V KB 、V KB and -V+V KB Three voltages (note that for the case of amorphous silicon TFTs, V KB Usually negative). However, the same supply provides +V, 0, and -V to the front electrode without any snap-back voltage offset. So, for example, when -V is provided to the front electrode, the maximum voltage of the display is 2V+V KB , the minimum voltage is V KB The waveform can be divided into several parts, providing positive voltage, negative voltage and V KB， Instead of using a separate power supply to provide V to the front electrode KB (It is costly and inconvenient).

[0115] Figure 6 An exemplary workflow of the controller is shown. The top workflow represents the conventional workflow of a dual particle system, as described in U.S. Patent No. 9,672,766, where the transitions from black to white and from white to black in the GC mode are approximately symmetrical. Therefore, switching between GC and DU modes as required by the use case (e.g., menus, scrolling, stylus writing, etc.) is very simple, with little accumulation of impulse potential, and thus no intermediate transition modes of the dual particle system are required.

[0116] However, in some multi-particle systems, such as ACeP®, the electrophoretic medium experiences large ghosting based on differential blurring when using symmetrical white-to-black and black-to-white transitions in GC mode. Therefore, when using conventional transition rules, when the device switches to DU (direct update) mode, the GC waveform is asymmetrical, resulting in impulse potential accumulation. However, with the present invention, i.e. Figure 6As shown in the bottom workflow, when switching between GC and DU modes of a multi-particle system, a transition pattern (DU_IN; DU_OUT) is used to compensate for the unbalanced impulse potential when moving between black and white states in GC mode. In one embodiment, the DU (direct update) mode sets the black and white states to very high impulse potentials (about 400V*frame), thereby ensuring that the display has a good black state and balanced impulse potential when operating in DU mode. Essentially, the present invention maintains the consistency of the black state impulse potential between DU and GC modes, while driving the white state with an impulse potential of the same magnitude and opposite sign as the black state in DU mode, and allows the white state to remain optically matched rather than impulse potential matched when transitioning between GC and DU modes.

[0117] Figure 7 A general visualization of the DUin and DUout modes is shown. Figure 7 In FIG. 1 , each state in a series of GC states is shown to transition to DU mode via a set of DUin waveforms that compensate for the impulse difference. In addition, when leaving DU mode, the display transitions back to GC mode, i.e., DUout mode, via a DUout waveform. Figure 7 The schematic diagram is general and is also particularly applicable to GC modes including 8, 16, 32, 64 or more color states. In most instances, the DU mode includes only white and black states, but other DU modes can also be achieved if the colored particles are selected correctly, such as green and white as DU states.

[0118] Figure 8 Example waveforms suitable for DU mode in a four-particle ACEP® system, which includes one white negatively charged particle and three (differently charged) positively charged cyan, yellow, and magenta particles, are shown. Although the waveforms are asymmetric (or opposite), the accumulated impulse (voltage*frame) for the transition from white to black (upper right waveform) and the transition from black to white (lower left waveform) is around 400V*frame. Therefore, in DU mode, the accumulated impulse potential is small when the pixel transitions between white and black. In some embodiments, duK and duW are independent controller states, and are transitions that a) maintain round-trip equilibrium and b) match the optical properties of the corresponding GC optical state. In addition, because most DU waveforms are driven with high voltage, pixel updates from black to white or white to black can be achieved in about 250 milliseconds. Although this update time is still a bit slow compared to the best (only) black and white electrophoretic displays, it is more than enough for page turning and stylus input.

[0119] As mentioned above, the transition patterns (DU_IN; DU_OUT) are needed so that the display does not generate excessive impulse potentials when moving between GC and DU modes, which would manifest as ghosting and also shorten the life of the backplane electronics. The structure imposed in these transitions is such that when DUin is used, the transition to duK is direct, i.e. flicker-free, single pulse, while enforcing light state matching between duK and K. In contrast, the conventional DU pattern keeps K->K as a null transition. Fig. 9A As shown, in the DUin scheme, duK->duK is empty, but K-.>duK is filled and is a direct transition. Fig. 9A A set of potential transition waveforms for DU_IN are shown with voltage on the Y-axis and frame number on the X-axis. It is noteworthy that many of the transitions are actually empty, i.e., no pulse is output. In general, DUin is applied when transitioning between text mode states (K, GT2, GT3, W) and DU states (duK, duW), which applies a transition with a net impulse equal to the duK impulse potential to go to duK. This is because in GC mode, the impulse potential of K is zero due to the associated clear pulse. The impulse potential of the W state in GC is also zero. Therefore, all transitions between white states are selected to maintain 0 net impulse potential. Finally, the transitions from gray tones to DU black and white maintain the net impulse potential of the original text mode. In order to understand the actual optical transitions experienced, Fig. 9A The waveforms were run on a simulator of a four-particle ACEP® system consisting of one negatively charged white particle and three (differently charged) positively charged cyan, yellow, and magenta particles. The resulting transitions are shown in Figure 2. Fig. 9B For an empty transition, there is no color change. However, for some transitions, such as from GC2 to duK and from GC2 to duW, the display will "flash" a few frames of bright colors (e.g., red, blue). However, since the DUin transition takes about 365 milliseconds, the color change is not particularly noticeable. Similarly, Fig. 10A and 10B represents one embodiment of various waveforms that may be used to transition from DU to GC (ie, DU_OUT mode). Likewise, some transitions, such as from duK to GC2, will transition through bright colors, but will not be noticeable due to the rapidity of the transition.

[0120] By adjusting the DUout transition to have a specific net impulse potential, the round-trip impulse balance from GC mode to DU mode and then back to GC mode is maintained. Specifically, Fig. 10AAs shown, transitions between DU states (duK, duW) and GC mode states (K, GC2, GC3, W) have a net impulse potential equal to the negative duK IP. The net impulse for the transition from duW to W / K is 0. In general, all transitions from DU states to GC states using DUout appear as if they switch to white before transitioning to the text mode state, as shown in Fig. 10B The complete transition time from DU to GC using DU_OUT is typically around 576 milliseconds.

[0121] Fig.11 An example of impulse potential calculation is shown in Fig.11 In , the four display pixels are represented as squares in the upper box, and the matrix for impulse potential balancing is represented in the lower box (i.e., the lower box is not a pixel). The starting state and final state use the GC mode, with two black pixels on the top and two white pixels on the bottom. As shown in the leftmost square, the impulse potential of the four pixels when they complete the last GC update is zero. In DU mode (represented by the two lower matrices in the middle), the transition from duW to duK produces a +1 impulse, while the transition from duK to duW produces a -1 impulse. It will be appreciated that +1 and -1 are arbitrary units. Use Figure 8 The waveform of the +1 is equivalent to about 400V*frame. An important point is that in DU mode, the transitions have the same impulse potential and opposite sign.

[0122] However, to accommodate the accounting for DU mode, the transition from K (i.e., the black state in GC mode) to duK in DU mode must also experience an impulse potential of +1. This is shown in the lower left matrix. This is not intuitive. In most existing technologies, the transition between black states from GC to DU does not add an additional impulse to the pixel. The transition from W to duK also requires an impulse potential of +1, but this is not surprising because the color state of the pixel needs to change. Nevertheless, if it were not for the increase in impulse potential for switching between states in DU mode, driving from white to black would not usually require so much impulse potential. As can be seen from the pixels in the three boxes in the middle, when the pixel moves between black and white in DU mode, the impulse potential will cycle until it switches back to GC mode. At this point, in order to eliminate ghosting in GC mode, it is necessary to eliminate any remaining impulse potential. Therefore, the DU output matrix shows that an impulse potential of -1 is required to go from duK to black or white.

[0123] As can be seen from the above, the method of changing the driving mode of the present invention can provide improved updates for color electrophoretic displays, thereby enabling device designers to create more interactive applications, thereby improving the practicality of devices containing such displays. It is obvious to those skilled in the art that a large number of changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the present invention. Therefore, the entire description above should be interpreted from an illustrative rather than a restrictive perspective.

Claims

1. A method of driving an electrophoretic display having a plurality of pixels, each pixel being capable of displaying at least three optical states, including white, black, and a color that is neither white nor black, the method comprising: driving the electrophoretic display with a first drive mode that allows transitions between all optical states; driving the electrophoretic display with a second drive mode that includes only transitions between black and white optical states, wherein in the second drive mode, the impulse potential experienced by the pixel when changing from the white state to the black state is equal in magnitude and opposite in sign to the impulse potential experienced by the pixel when changing from the black state to the white state; driving the electrophoretic display with a first transition mode that allows transitioning from a color state of the first drive mode to a white state or a black state of the second drive mode, wherein the first transition mode compensates for excess impulse potential that would be delivered to the pixel in the second drive mode; and The electrophoretic display is driven with a second transition pattern that allows transition from a white state or a black state of the second drive mode to a color state of the first drive mode, wherein the second transition pattern compensates for excess impulse potential delivered to the pixel in the second drive mode.

2. The method according to claim 1, wherein: In the first driving mode, the impulse potential experienced by the pixel when changing from the white state to the black state is different in magnitude from the impulse potential experienced by the pixel when changing from the black state to the white state, and has an opposite sign.

3. The method according to claim 1, wherein: The first transition pattern and the second transition pattern do not have the same impulse potential compensation between a color state of the first drive mode and a white state of the second drive mode and between a color state of the first drive mode and a black state of the second drive mode.

4. The method according to claim 1, wherein: The first transition pattern and the second transition pattern do not have the same waveform between a color state of the first driving mode and a white state of the second driving mode and between a color state of the first driving mode and a black state of the second driving mode.

5. The method according to claim 1, wherein: In the second driving state, the waveform causing the transition from the white state to the black state includes at least five frames of maximum positive voltage.

6. The method according to claim 1, wherein: In the second driving state, the waveform causing the transition from the black state to the white state includes at least five frames of maximum negative voltage.

7. The method according to claim 1, wherein: The first driving mode is DC balanced.

8. The method according to claim 1, wherein: The first transition pattern and the second transition pattern are not DC balanced.

9. The method according to claim 1, wherein: Each pixel is capable of displaying at least eight optical states, and the first transition mode allows transitions from each of six non-black and non-white colored optical states to either a white state or a black state of the second drive mode.

10. The method according to claim 9, wherein: The eight optical states are black, white, red, magenta, yellow, green, cyan, and blue.

11. A display controller configured to execute the method according to claim 1.

12. An electrophoretic display configured to implement the method according to claim 1.

13. The display according to claim 12, wherein: The electrophoretic display includes an electrophoretic medium including at least three types of particles having different electrophoretic mobilities.

14. The display according to claim 13, wherein: At least two of the three types of particles have the same charge, but the magnitude of the charge is different.

15. The display according to claim 13, wherein: One particle type is negatively charged and appears white.

16. The display of claim 15, further comprising three types of positively charged particles, wherein: Each type of positively charged particle is partially light absorbing and has a different color than other types of positively charged particles.

17. The display according to claim 12, wherein: The electrophoretic medium is confined within a plurality of capsules or a plurality of microcells.

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