Electrophoretic display device

Abstract

An electrophoretic display device is provided in which the electrophoretic medium comprises a fluid and particles of four different colors, first, second, third and fourth types (W, Y, R, B). The first and third particles have one polarity of charge, while the second and fourth particles have the opposite polarity of charge; the first particles have a greater electrophoretic mobility or electrokinetic potential than the third particles, and the second particles have a greater electrophoretic mobility or electrokinetic potential than the fourth particles. One of the particles is white (W), one of the non-white particles (B) is partially light-transmissive, and the other two non-white particles (R, Y) are light-reflective. A third light-reflective particle (G) can be added to create a five-particle medium.

Description

[0001] This application is a divisional application of the application filed on June 4, 2021, with application number 202180038425.X and title "Electrophoretic Display Device". Citation of relevant applications

[0002] This application relates to U.S. Patent Nos. 9,170,468; 9,361,836; 9,513,527; 9,541,814; 9,640,119; 9,812,073; 9,922,603; 10,147,366; 10,234,742; 10,431,168; 10,509,293; 10,586,499; and 10,782,586.

[0003] The entire contents of the aforementioned provisional application and patent, as well as the entire contents of all other U.S. patents, published and co-pending applications mentioned below, are incorporated herein by reference. Background Technology

[0004] The aforementioned patents and published applications describe electrophoretic media, methods for driving such media, and electrophoretic display devices incorporating such media. Electrophoretic media comprises a fluid and particles of first, second, third, and fourth types dispersed in the fluid; such media may be referred to hereinafter as a "four-particle electrophoretic media." In some cases, the media also includes a fifth type of particles. These four or five types of particles have different optical properties (typically color) from each other. The first type of particles carries a high positive charge, and the second type carries a high negative charge. The third type carries a low positive charge, and the fourth type carries a low negative charge. (The charge intensity is measured based on the zeta potential.) The fifth type carries a medium charge of either polarity. In an electrophoretic display device, the electrophoretic media is disposed between a front electrode and a rear electrode, typically viewed from the front electrode (observation) side of the display. In a typical multi-pixel display, the front electrode is continuous, extending across multiple pixels and typically the entire display, while a separate rear electrode is provided for each pixel to control the displayed color pixel-by-pixel.

[0005] The optical properties of the first and second types of particles can (in principle) be displayed on the observation side by applying a high electric field of appropriate polarity to the electrophoretic medium for a period of time sufficient to position the first or second type of particles near the front electrode. To display the optical properties of the third type of particles, the second type of particles are first driven onto the observation surface by applying a high electric field of appropriate polarity, and then a low electric field of opposite polarity is applied to position the third type of particles near the observation surface, while the first, second, and fourth type of particles are separated from the surface. (Note that the second part of this sequence involves a change from the optical properties of highly negative particles (second type of particles) to the optical properties of low positive particles (third type of particles). Similarly, to display the optical properties of the fourth type of particles, the first type of particles are first driven onto the observation surface by applying a high electric field of appropriate polarity, and then a low electric field of opposite polarity is applied to position the fourth type of particles near the observation surface, while the first, second, and third type of particles are separated from the surface. (Again, note that the second part of this sequence involves a change from the optical properties of highly positive particles (first type of particles) to the optical properties of low negative particles (fourth type of particles). To display the color of intermediate charged particles, low-charged particles of opposite polarity are first driven onto the observation surface, and then an intermediate electric field with a polarity that drives the intermediate charged particles toward the observation surface is applied. (Again, the final step involves a change in the optical properties from those of a low-charged particle to those of an intermediate-charged particle of opposite polarity.) In practice, to achieve optimal separation of various particle types, the waveform (driving pulse sequence) can be far more complex than implied by the preceding brief overview and can include any one or more of the following: (a) repetition of one or two basic driving pulses already described; (b) zero-voltage time intervals between driving pulses; (c) the use of vibrating pulses (rapidly alternating positive and negative pulses) designed to uniformly mix the various particle types; and (d) DC balancing pulses designed to make the overall pulse of the waveform zero or close to zero (it is well known that repeatedly applying an unbalanced DC waveform to an electrophoretic display can eventually damage the display, potentially degrading the quality of the displayed image and possibly ultimately causing the display to fail completely). For all the aforementioned waveform characteristics, see, for example, the aforementioned U.S. Patent No. 9,640,119.

[0006] Although not explicitly stated in most cases, four-particle and five-particle electrophoretic media use light-scattering ("reflective") particles instead of light-transmitting particles. Therefore, the color (or other optical properties) seen on the observation side is determined solely by the color of the particle immediately adjacent to the front electrode; the relative positions of other particles are irrelevant. Consequently, such electrophoretic media exhibit only four or five independent optical states, although they may also display "particle-mixing" states (typically gray) where various types of particles are randomly mixed, as well as other mixed states where two types of particles are located near the observation side; for example, orange can be produced by mixing red and yellow particles near the observation surface.

[0007] Limiting four-particle electrophoretic media to four independent optical states is a significant practical drawback because many applications, such as electronic signs like electronic shelf labels, require the ability to display black, white, and three primary colors, such as red, green, and blue, or blue, red, and yellow. A good black-and-white state is important for text, while the three primary colors allow for full-color display through dithering. To date, four-particle electrophoretic media typically have good black and white as well as two “highlight” colors (usually red and yellow), or white and the three primary colors, relying on mixing the three primary colors to produce a (often unsatisfactory) “processed” black.

[0008] The aforementioned drawbacks of four-particle electrophoretic media are known to be overcome by incorporating fifth and optional sixth types of particles into the electrophoretic medium; see, for example, U.S. Patent Nos. 9,541,814 and 9,922,603. However, increasing the number of particle types in the electrophoretic medium makes the selection of suitable particles more difficult due to the increased need for strict control over the charge on various particles, the increased possibility of interactions between various particles (which may lead to increased color contamination), and the elongated waveform; the five-particle and six-particle electrophoretic media described in U.S. Patent Nos. 9,541,814 and 9,922,603 ​​require at least one third-order waveform, where, in order to display the color of an intermediate charged particle of one polarity, it is first necessary to display the color of a highly charged particle of one polarity, then the color of a low charged particle of the opposite polarity, and finally the color of an intermediate charged particle of one polarity.

[0009] The inventors have now discovered that a four-particle electrophoretic medium can display five separate optical states by selectively allowing partial light transmission of one of the particle types. A fifth particle can be added to allow the display of six optical states, such as black, white, red, green, blue, and yellow. (In practice, this sixth optical state is desirable because the black / white / red / green / blue system typically does not provide good saturation of yellow, while the black / white / blue / red / yellow system does not provide good saturation of green.) Summary of the Invention

[0010] Therefore, the present invention provides an electrophoretic medium comprising a fluid and particles of first, second, third, and fourth types dispersed in the fluid, the particles of the first, second, third, and fourth types having first, second, third, and fourth colors respectively, the particles of the first and third types having a single polarity of charge, while the particles of the second and fourth types have opposite polarities of charge, the particles of the first type having a greater electromotive force or electrophoretic mobility than the particles of the third type, and the particles of the second type having a greater electromotive force or electrophoretic mobility than the particles of the fourth type, wherein one type of particle is white, one type of non-white particle is partially translucent, and the other two types of non-white particles are light-reflective. The electrophoretic medium may further include a fifth type of charged particles having a fifth color different from all the first, second, third, and fourth colors. In some embodiments, the fifth type of particles are light-reflective and carry a charge of the same polarity as the particles of the partially translucent type. In some embodiments, the fifth type of particles have a greater electromotive force or electrophoretic mobility than the other two types of particles with the same polarity of charge.

[0011] In some embodiments of the invention, the white-type particles are third or fourth-type particles, i.e., one of the low-charge types. Furthermore, when the white particles are one of the low-charge types, the partially translucent particles can be high-charge (or medium-charge, if five charged particles are present) particles with the opposite polarity to the white particles. In this case, it is advantageous that the light-reflecting particles (or one of the five particle systems) having the same charge as the partially translucent particles possess optical properties such that the mixture of the two types of particles substantially absorbs all visible radiation, i.e., provides process black.

[0012] In the electrophoretic medium of this invention, the fourth particle may be white, the second particle may be yellow, and the first and third particles may be red and blue (in any order), although for the purposes of the following reference... Figures 6A-6F The reason for this discussion is that it may be advantageous for the first particle to be red and partially translucent. If present, the fifth particle could be, for example, green, cyan, or magenta, although green is generally preferred for the reasons mentioned above.

[0013] The four-particle electrophoretic medium of this invention can display at least five colors (excluding a completely mixed state of random mixing of the four types of particles). The colors of white particles and the two light-reflecting types of particles can be simply displayed by placing each type of particle near the observation surface. The color of partially translucent particles can be displayed by placing a mixture of this type of particle and white particles near the observation surface, such that light entering the observation surface is scattered by the white particles and passes through the partially translucent particles, ultimately reappearing from the observation surface in the color of the translucent type of particles. (See reference below) Figure 3A A discussion of the actual details of this color formation. The fifth color displayed is processed black, achieved by placing translucent particles near the observation surface, followed immediately by reflective particles with the same polarity of charge (i.e., on the opposite side of the observation surface adjacent to the translucent particles). This allows light entering through the observation surface to pass through the translucent particles and then be substantially completely absorbed by the reflective particles immediately following them. Clearly, for this processed black to be satisfactory, the combined absorption of these two types of particles must extend across the entire visible spectrum; this is why these two particles are preferably red and blue (in any order), as it is relatively easy to arrange red and blue particles together to absorb all visible light. Examples of absorption spectra of red and blue pigments capable of producing excellent processed black are given below. Some four-particle electrophoretic media of the present invention can effectively display a sixth color by placing a mixture of two non-white light-reflecting particles near the observation surface; green is produced when these two types of particles are yellow and blue. The five-particle media of the present invention can display six colors, with the additional color being the color of the third non-white reflective particle.

[0014] As previously described, in the electrophoretic medium of this invention, one type of particle is white, another type is partially transparent, and the remaining two or three types of particles are light-reflective (i.e., light-scattering). In practice, completely light-scattering particles or completely non-light-scattering transparent particles certainly do not exist. The minimum degree of light scattering in light-scattering particles and the maximum tolerable degree of light scattering in transparent particles can vary depending on factors such as the exact pigments used, their refractive index and size, their color, the thickness of the particle layer in question (which itself depends on the thickness of the electrophoretic medium layer and the loading of each type of particle in the medium), and the user's or application's ability to tolerate some deviation from the desired color. The scattering and absorption properties of pigments can be evaluated by measuring the diffuse reflectance of a pigment sample dispersed in a suitable matrix or liquid against white and dark backgrounds. Results from such measurements can be interpreted according to many models well known in the art (e.g., the one-dimensional Kubelka-Munk treatment).

[0015] The transmittance of a pigment is most conveniently measured by contrast, which (for the purposes of this application) is defined as the ratio of the light reflectance of a sample backed by a black material with a specific reflectance (Rb) to the reflectance of the same sample backed by a white material with a specified reflectance (Rw):

[0016] CR = Rb / Rw

[0017] Contrast ratio (CR) is an indicator of opacity and naturally varies with the thickness of the pigment layer present in the electrophoretic medium and the type of pigment used. Typically, you will obtain complete opacity at CR = 0.98. The hiding power of a paint is understood as its ability to eliminate the contrast between a black and white substrate to the extent that the reflectivity obtained on a black substrate is 98% of the reflectivity obtained on a white substrate. The contrast ratio of the translucent pigment layer used in the electrophoretic medium of this invention should be no greater than about 0.5, preferably no greater than 0.3. The blue pigment used in the experiments described below has a contrast ratio of about 0.2. The contrast ratio of the reflective pigment should be no less than about 0.6, preferably no less than about 0.7.

[0018] The electrophoretic medium of the present invention may be encapsulated or unencapsulated. If encapsulated, the electrophoretic medium may be contained within multiple microunits, as described in U.S. Patent No. 6,930,818, the contents of which are incorporated herein by reference in their entirety. The display unit may also be other types of microcontainers, such as microcapsules, microchannels, or equivalents, regardless of their shape or size. Alternatively, the electrophoretic medium may be encapsulated within a capsule, or may be in the form of a so-called polymer-dispersed electrophoretic medium comprising multiple discrete droplets of electrophoretic fluid and a continuous phase of polymeric material; even without discrete capsule membranes associated with each individual droplet, discrete droplets of electrophoretic fluid in such a polymer-dispersed electrophoretic display may be considered as capsules or microcapsules; see, for example, U.S. Patent No. 6,866,760.

[0019] This invention extends to an electrophoretic display device, comprising the electrophoretic dielectric layer of this invention, a front electrode and a rear electrode disposed on opposite sides of the electrophoretic dielectric layer, and a voltage control device configured to control the potentials of the front electrode and the rear electrode. This invention also extends to a front planar laminate, an inverted front planar laminate, or a double-release film comprising the electrophoretic dielectric layer of this invention; the definitions of the front planar laminate, the inverted front planar laminate, and the double-release film are given below.

[0020] The present invention also extends to a method for driving the electrophoretic display device of the present invention. The first driving method includes:

[0021] (i) During a first time period, a first driving voltage is applied that drives partially transparent particles and light-reflecting particles with the same polarity as the partially transparent particles toward the observation surface;

[0022] (ii) After step (i), no driving voltage is applied during a second time period that is longer than the first time period;

[0023] (iii) Repeat steps (i) and (ii) so that the color (preferably black) of the mixture of the two types of particles is displayed on the observation surface.

[0024] The second driving method includes:

[0025] (i) Applying a second driving voltage with polarity that drives particles of the partially transparent type toward the observation surface during the third time period;

[0026] (ii) Apply a third driving voltage with opposite polarity and smaller amplitude than the second driving voltage during a fourth time period that is longer than the third time period;

[0027] (iii) Repeat steps (i) and (ii);

[0028] (iv) After repeating steps (i) and (ii), apply a third driving voltage during the fifth time period;

[0029] (v) No driving voltage is applied during the sixth time period;

[0030] (vi) Repeat steps (iv) and (iv);

[0031] (vii) After repeating steps (iv) and (v), a second driving voltage is applied during the seventh time period;

[0032] (viii) Applying a fourth driving voltage with the same polarity as the third driving voltage but a smaller amplitude during an eighth time period longer than the seventh time period; and

[0033] (ix) Repeat steps (vii) and (viii), but end with repeating step (vii) instead of repeating step (viii), thereby displaying the color of the light-transmitting type of particles on the observed surface.

[0034] In this second driving method, a zero-voltage time period may be inserted between each step (i) and the subsequent step (ii) and / or between each step (vii) and the subsequent step (viii).

[0035] The third driving method of the present invention includes:

[0036] (i) During the ninth time period, a fifth driving voltage is applied that drives two types of particles of one polarity toward the observation surface;

[0037] (ii) Apply a sixth driving voltage with the opposite polarity to the fifth driving voltage and a smaller amplitude than the fifth driving voltage during a tenth time period that is longer than the ninth time period;

[0038] (iii) Repeat steps (i) and (ii); and

[0039] (iv) After repeating steps (i) and (ii), a sixth driving voltage with the same polarity as the fourth driving voltage is applied, the magnitude and / or duration of which the sixth driving voltage is applied is insufficient to drive the display to show the color of the second type of particles on the observation surface, thereby showing the color of a mixture of two non-white light-reflecting particles on the observation surface.

[0040] In this third driving method, a zero-voltage time period can be inserted between each step (i) and the subsequent step (ii).

[0041] Each driving method of the present invention can reduce or eliminate the total impulse of the applied total waveform by having one or more time periods prior to the vibration waveform and / or one or more time periods of the DC balanced waveform (i.e., the time period during which a non-zero voltage is applied to the display).

[0042] In any driving method of the present invention, when the driving pulse sequence is repeated, the repetition can continue for at least 4 times, preferably at least 8 times. Attached Figure Description

[0043] The attached image Figure 1 This is a schematic cross-section of the four-particle display device of the present invention.

[0044] Figure 2 It shows the use of Figure 1 The preferred absorption spectrum of pigment particles for display devices.

[0045] Figures 3A-3F It is similar to Figure 1 A schematic cross-section, but showing Figure 1 Display devices can undergo a variety of optical transformations.

[0046] Figure 4 The DC balance waveform and vibration waveform that can be incorporated into the driving method of the present invention are shown.

[0047] Figures 5A-5F It shows that it can be used to execute separately Figures 3A-3F The waveform of the transition shown.

[0048] Figures 6A-6F It is similar to Figures 3A-3F A schematic cross-section, but showing various optical transitions in a display device using the red portion of the transparent particles.

[0049] Figures 7A-7F It is similar to Figures 3A-3F The diagram shows a schematic cross-section, but illustrates the various optical transitions that the five-particle display device of the present invention can undergo.

[0050] Figure 8A and 8B It shows that it can be used to perform, such as Figure 7E and 7F The waveform of the transition is shown. Detailed Implementation

[0051] As described above, in one aspect, the present invention provides a four-particle electrophoretic medium that can be configured to display five separate optical states. The electrophoretic medium comprises a fluid and first, second, third, and fourth types of particles dispersed in the fluid; all four types of particles have different colors. The first and third types of particles carry a single polarity of charge, while the second and fourth types of particles carry opposite polarities of charge. The first type of particles has a greater electromotive force or electrophoretic mobility than the third type of particles, and the second type of particles has a greater electromotive force or electrophoretic mobility than the fourth type of particles. (Therefore, in two pairs of oppositely charged particles, one carries a stronger charge than the other pair. Thus, the four types of particles can also be referred to as highly positive particles, highly negative particles, low-positive particles, and low-negative particles.) One type of particle is white. One type of non-white particle is partially translucent, while the other two types of non-white particles are reflective.

[0052] like Figure 1 In the example shown, the blue particle (B) and the yellow particle (Y) are the first pair of particles with opposite charges, in which the blue particle is a highly positive particle and the yellow particle is a highly negative particle. The red particle (R) and the white particle (W) are the second pair of particles with opposite charges, in which the red particle is a low-positive particle and the white particle is a low-negative particle. It should be understood that the polarity of the above charges can be reversed and the display will continue to function in the same way, except that the polarity of the driving waveform described below needs to be reversed.

[0053] White particles can be formed from inorganic pigments, such as TiO2, ZrO2, ZnO, Al2O3, Sb2O3, BaSO4, or PbSO4.

[0054] Non-white and non-black particles are independent of colors such as red, green, blue, magenta, cyan, or yellow. Pigments used for colored particles may include, but are not limited to, CI pigments PR254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY83, PY138, PY150, PY155, or PY20. These are commonly used organic pigments described in the color index manuals “New Pigment Application Technology” (CMC Publishing Co, Ltd, 1986) and “Printing Ink Technology” (CMC Publishing Co, Ltd, 1984). Specific examples include Clariant's Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV Fast Red D3G, Hostaperm Red D3G 70, Hostaperm Blue B2G-EDS, Hostaperm Yellow H4G-EDS, Novoperm Yellow HR-70-EDS, Hostaperm Green GNX, BASF Irgazine Red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; and Sun Chemical's Phthalocyanine Blue, Phthalocyanine Green, Aniline Yellow, or Aniline AAOT Yellow. For use in... Figure 1 The preferred translucent blue pigment for the display is Kremer 45030, "Ultramarine Blue, Super Green," a sodium aluminum thiosilicate pigment, CI Pigment Blue 29:77007, purchased from Kremer Pigmente GmbH & Co. KG, Hauptstr. 41-47, DE-88317 Aichstetten, Germany. This translucent blue pigment can be used in combination with the aforementioned Hostaperm Red D3G 70 pigment.

[0055] like Figure 2 As shown, this blue pigment has peak transmittance at approximately 450 nm and significant transmittance in the visible light range from 400 to approximately 530 nm. On the other hand, Hostaperm Red D3G 70 pigment is essentially non-reflective below approximately 555 nm. Therefore, when the two pigments are... Figure 3AIn the arrangement shown, the translucent blue pigment is adjacent to the observation surface, while the reflective red pigment is adjacent to the opposite side of the blue pigment on the observation surface. All visible radiation entering through the observation surface and passing through the blue pigment will be absorbed by the red pigment, and the observation surface will appear black.

[0056] Non-white particles can also be inorganic pigments, such as red, green, blue, and yellow. Examples may include, but are not limited to, CI Pigment Blue 28, CI Pigment Green 50, and CI Pigment Yellow 227.

[0057] In addition to color, these four types of particles can have other different optical properties, such as light transmission, reflection, and emission, or, in the case of displays used for machine reading, pseudocolor in the sense of variations in reflectivity at electromagnetic wavelengths outside the visible light range.

[0058] The display layer for displaying fluids using the present invention, such as Figure 1 As shown, the display layer has two surfaces: a first surface (13) on the viewing side and a second surface (14) on the opposite side of the first surface (13). A display fluid is sandwiched between the two surfaces. On one side of the first surface (13), there is a common electrode (11), which is a transparent electrode layer (e.g., ITO) covering the entire top of the display layer. On one side of the second surface (14), there is an electrode layer (12) comprising a plurality of pixel electrodes (12a). However, the invention is not limited to any particular electrode configuration.

[0059] Pixel electrodes are described in U.S. Patent No. 7,046,228, the contents of which are incorporated herein by reference in their entirety. It is worth noting that while active matrix driving using a thin-film transistor (TFT) backplane is mentioned for the pixel electrode layer, the scope of this invention includes other types of electrode addressing, provided the electrodes provide the required functionality.

[0060] Figure 1 Each space between the two vertical dashed lines represents a pixel. As shown, each pixel has a corresponding pixel electrode. An electric field is created for the pixel by the potential difference between the voltage applied to the common electrode and the voltage applied to the corresponding pixel electrode. (Note that in the various waveforms shown in the attached figures, the potential difference plotted is the potential difference applied to pixel electrode 12a; typically, it is assumed that the common electrode is held at ground voltage. Since the color displayed by the pixel depends on the particles adjacent to the common electrode 11, when a positive potential difference is shown in the figure, the common electrode is negative relative to the pixel electrode, and positively charged particles are attracted to the common electrode.)

[0061] The solvent for dispersing the four types of particles is colorless and transparent. It preferably has a low viscosity and a dielectric constant in the range of about 2 to about 30, preferably about 2 to about 15, to obtain high particle mobility. Examples of suitable dielectric solvents include hydrocarbons such as Isopar®, DECALIN, 5-ethylidene-2-norbornene, fatty oils, paraffin oils, and silicone liquids; aromatics such as toluene, xylene, diarylethane, dodecylbenzene, or alkylnaphthalene; halogenated solvents such as perfluoronaphthene, perfluorotoluene, perfluoroxylene, dichlorotrifluorotoluene, 3,4,5-trichlorotrifluorotoluene, monochloropentafluorobenzene, dichlorononane, or pentachlorobenzene; perfluorinated solvents such as FC-43, FC-70, or FC-5060 from 3M Company, St. Paul MN; low molecular weight halogens containing polymers such as poly(fluoropropylene oxide) from TCI America, Portland, Oregon; and halogenated solvents such as poly(trifluorochloroethylene) from Halocarbon Product Corp., River Edge, NJ; and low molecular weight halogens such as Galden from Ausimont or Krytox Oils and Greases K-Fluid from DuPont, Delaware. Series of perfluoropolyethers, from Dow-corning's polydimethylsiloxane-based silicone oil (DC-200).

[0062] In one embodiment, the charge carried by the "low-charge" particle may be less than about 50% of the charge carried by the "high-charge" particle, preferably about 5% to about 30%. In another embodiment, the "low-charge" particle may carry less than about 75%, or about 15% to about 55% of the charge carried by the "high-charge" particle. In yet another embodiment, the comparison of charge levels shown applies to two types of particles having the same charge polarity.

[0063] The charge intensity can be measured based on the electromotive force (EMF). In one embodiment, the EMF is determined using a Colloidal Dynamics AcoustoSizer IIM, ESA EN# Attn flow-through electrolytic cell (K:127) with a CSPU-100 signal processing unit. Instrument constants at the test temperature (25ºC) are entered before testing, such as the density of the solvent used in the sample, the dielectric constant of the solvent, the velocity of sound in the solvent, and the viscosity of the solvent. The pigment sample is dispersed in a solvent (which is typically a hydrocarbon fluid with fewer than 12 carbon atoms) and diluted by weight to 5-10%. The sample also contains a charge modifier (Solsperse 19K, available from Berkshire Hathaway, Lubrizol Corporation; "Solsperse" is a registered trademark) with a charge modifier-to-particle weight ratio of 1:10. The mass of the diluted sample is determined, and the sample is then loaded into the flow-through electrolytic cell to determine the EMF.

[0064] The amplitudes of "highly positive" and "highly negative" particles can be the same or different. Similarly, the amplitudes of "lowly positive" and "lowly negative" particles can be the same or different. However, the electromotive force of a "highly positive" particle, or a positive particle with a larger charge intensity or magnitude, is greater than that of a "lowly positive" particle, or a positive particle with a smaller charge intensity or magnitude. The same logic applies to "highly negative" and "lowly negative" particles. In the same medium and in the same field, higher-charged particles have greater electrophoretic mobility; that is, higher-charged particles travel the same distance in a shorter time than lower-charged particles.

[0065] It should also be noted that in the same fluid, two pairs of high and low charged particles may have different degrees of charge difference. For example, in one pair, the charge intensity of the low positively charged particle may be 30% of the charge intensity of the high positively charged particle, while in another pair, the charge intensity of the low negatively charged particle may be 50% of the charge intensity of the high negatively charged particle.

[0066] The following example illustrates a display device that uses this type of display fluid.

[0067] Example

[0068] Figures 3A-3F This example demonstrates the following: High positive transmittance particles are blue (B); high negative transmittance particles are yellow (Y); low positive transmittance particles are red (R); and low negative transmittance particles are white (W). Figure 3AThe transition shown begins from a fully mixed state, denoted as "(M)," and is generated by applying vibrational pulses as described below. When alternating pulses of high positive potential difference (e.g., +15V) and no potential difference (0V) are applied to pixel electrode 22a for a sufficiently long period, blue (B) and red (R) particles are driven toward the common electrode (21) or the viewing side, while yellow and white particles are driven toward the pixel electrode 22a side. Red (R) and white (W) particles move more slowly than the highly charged blue and yellow particles due to their weaker charge. Therefore, blue particles are close to the common electrode, and red particles are close to them below (e.g., ...). Figure 3A (As shown). Due to the reasons already discussed above, this causes the pixels to appear black, in Figure 3A The symbol is represented as "(K)"; white and yellow particles are masked by reflective red particles without affecting the displayed color.

[0069] Similarly, Figure 3B The transition shown begins in a fully mixed state (M), which is generated by applying vibrational pulses as described below. When alternating pulses of high negative potential difference (e.g., -15V) and no voltage (0V) are applied to pixel electrode 22a for a sufficiently long period, blue (B) and red (R) particles are driven toward pixel electrode 22a, and yellow and white particles are driven toward the common electrode side. Red (R) and white (W) particles, carrying a weaker charge, move more slowly than the highly charged blue and yellow particles. As a result, reflective yellow particles are placed close to the common electrode, causing the pixel to appear yellow. Figure 3B The color is represented as "(Y)"; white, red, and blue particles are masked by reflective yellow particles, without affecting the displayed color. Although yellow can theoretically be generated by alternating pulses of -15V and 0V, more complex waveforms are preferred in practice, as shown in the reference below. Figure 5B As stated above.

[0070] Figure 3CThe transition shown begins in a fully mixed state (M). When alternating pulses of high negative potential difference (e.g., -15V) and low positive potential difference (e.g., +8V), where the low positive pulse is much longer than the high negative pulse, are applied to pixel electrode 22a for a sufficiently long period, red (R) particles are driven toward the common electrode 21 side, and white particles (W) are driven toward the pixel electrode 22a side. The oscillating electric field causes the highly charged blue and yellow particles to repeatedly pass each other in the middle of the electrophoretic layer thickness. The strong electrostatic attraction between the highly charged positive and negative particles greatly slows down the movement of these particles and tends to keep them in the middle of the electrophoretic layer thickness. However, the electric field generated by the low positive pulse is sufficient to separate the low-charge white and red particles, thus allowing the low positive red particles (R) to move all the way to the common electrode 21 side and the low negative white particles to move toward the pixel electrode 22a side. As a result, the reflected red particles are close to the common electrode, causing the pixel to appear red. Figure 3C The symbol is represented as "(R)"; white, yellow, and blue particles are masked by reflective red particles without affecting the displayed color. Importantly, this system allows for the separation of weaker charged particles from stronger charged particles of opposite polarity.

[0071] Figure 3D The transition shown begins in a fully mixed state (M). When alternating pulses of high positive potential difference (e.g., +15V) and low negative potential difference (e.g., -8V), where the low negative pulse is much longer than the high positive pulse, are applied to pixel electrode 22a for a sufficiently long period, red (R) particles are driven toward pixel electrode 22a, and white particles (W) are driven toward common electrode 21. Figure 3C The transition shown is that the oscillating electric field keeps the highly charged blue and yellow particles together in the middle of the electrophoretic layer thickness. However, the electric field generated by the low negative pulse is sufficient to separate the low-charged white and red particles, allowing the low positive red particles (R) to move all the way to the pixel electrode 22a side and the low negative white particles to move to the common electrode 21 side. As a result, the white particles are close to the common electrode, causing the pixel to appear white. Figure 3D The white particle is represented as "(W)"; red, yellow, and blue particles are masked by white particles, without affecting the displayed color. While white can theoretically be generated by alternating pulses of +15V and -8V, more complex waveforms are preferred in practice, as shown in the reference below. Figure 5D As stated above.

[0072] Figure 3E The transformation shown is from Figure 3D The device begins in the white state (W). A positive potential difference pulse is applied to the device in this state, but the total impulse is insufficient to drive the device to... Figure 3AThe black state (K) is shown in the diagram. A positive pulse causes the highly charged blue particles to move toward the common electrode 21 side, and the white particles to move toward the pixel electrode 22a side. However, since the highly charged blue particles move faster than the low-charged white particles, the mixture of blue and white particles is visible through the viewing surface, thus the pixel appears blue.

[0073] from Figure 3E First, it can be seen that the blue saturation observed at the observation surface will be significantly reduced due to reflection from the white pigment immediately adjacent to the front electrode. However, it should be understood that... Figure 3E (as well as Figures 3A-3D (3F, 6A-6F, and 7A-7F) are all highly illustrative. In practice, pigment particles are not spherical (because the crystalline pigments used preferentially break along certain crystal planes—for example, rutile titanium dioxide, commonly used as a white pigment in electrophoresis, is tetragonal and tends to form square prisms), the particles vary significantly in size, the "reflection" from white particles is essentially Lambertian scattering rather than specular reflection, and there are differences compared to... Figure 3E The diagram shows multiple layers of particles. (The exact number of layers depends, of course, on the particle load in the electrophoretic medium, the thickness of the medium, and the size of individual particles, but in practice, there are usually at least 5-10 layers.) The overall effect of all these factors is that only a small fraction of the visible light entering the electrophoretic medium through the observation surface is directly reflected back to the observation surface by the white particles, resulting in a very good saturated blue in practice.

[0074] In addition, although Figure 3A It shows blue and red particles in completely separated layers, while Figure 3E The diagram shows a complete mixture of blue and white particles, but it is understood that these represent two extreme states and in practice can be a continuous gradient between completely separated layers and a complete mixture. The invention is not limited to any theoretical explanation regarding the exact location of the particles and their degree of mixing with other particles, as long as the desired color is obtained.

[0075] at last, Figure 3F The transformation shown is from Figure 3C The red state (R) is shown as the starting point. A negative potential difference pulse is applied to the device in this state, but the total impulse is insufficient to drive the device to... Figure 3B The yellow state (Y) is shown in the diagram. A negative pulse causes high negative yellow particles to move toward the common electrode (21), while low positive red particles move much more slowly toward the pixel electrode (22a). The result is a mixture of red and yellow particles visible through the common electrode 21 and the pixel appears orange.

[0076] To ensure color brightness and purity, a DC balancing and / or vibration waveform can be used before any of the aforementioned transitions. The vibration waveform consists of repeating a pair of opposite drive pulses many times. For example, the vibration waveform could consist of a +15V pulse lasting 20 milliseconds and a -15V pulse lasting 20 milliseconds, with such a pair of pulses repeated 50 times. The total duration of this vibration waveform is 2000 milliseconds. In practice, a single vibration pulse may have at least 10 repetitions (i.e., ten pairs of positive and negative pulses). The vibration waveform can be applied before the drive voltage is applied, regardless of the optical state (black, white, red, or yellow). After applying the vibration waveform, the optical state will not be pure white, pure black, pure yellow, or pure red. Instead, the color state will be a mixture of four types of pigment particles.

[0077] The application time of each driving pulse in the vibration waveform does not exceed 50% (or no more than 30%, 10%, or 5%) of the driving time required for a complete color transition from one highly charged particle to another (blue to yellow in this example, and vice versa). For example, if it takes 300 milliseconds to drive the display device from a completely black state to a completely yellow state, or vice versa, the vibration waveform can consist of positive and negative pulses, each with an application time not exceeding 150 milliseconds. In practice, shorter pulses are preferred. The described vibration waveform can be used in the driving method of the present invention. Throughout all the figures of this application, the vibration waveform is shortened (i.e., the number of pulses is less than the actual number).

[0078] A DC-balanced waveform is designed to reduce the overall impulse of the entire waveform (i.e., the voltage integral over time) to a small value, if possible, zero. As discussed, for example, in U.S. Patent Nos. 6,531,997 and 6,504,524, problems may arise and the display's lifespan may be reduced if the method used to drive the display does not result in a net time-averaged applied electric field across the electro-optic medium of zero or near zero. A waveform that does indeed result in a zero net time-averaged applied electric field across the electro-optic medium is conveniently referred to as a "DC-balanced" or "DC-balanced" waveform.

[0079] Figure 4 The combined DC balancing / vibration waveform is shown, including a DC balancing portion 42, followed by a vibration portion 44. Although Figure 4 The DC balancing section 42 is shown as having a high positive potential difference, but it should be understood that the DC balancing section can have a high or low, positive or negative potential difference or a zero potential difference, depending on the impulse of the rest of the applied waveform.

[0080] In addition, although Figure 4A single DC balancing section is shown, followed by a single oscillating section, but a combined DC balancing / oscillating waveform can contain multiple DC balancing sections and multiple oscillating sections that alternate with each other, and can begin and end at either a DC balancing section or an oscillating section. Using multiple DC balancing sections can be advantageous because by setting one or more DC balancing sections to high voltage and setting one or more to zero, for example, a total waveform impulse closer to zero can be achieved compared to using a single DC balancing section. The durations and applied potential differences of the multiple DC balancing sections may differ from each other. Similarly, multiple oscillating sections may differ from each other in terms of duration, amplitude of the potential difference, and frequency.

[0081] Figure 5A The following diagram illustrates the implementation. Figure 3A The transformation produces a waveform in a black optical state; this waveform is an example of the first driving method of the present invention. Under a high negative voltage VH2, after a DC balancing period of duration t1 and a vibrational period S, a mixed state M is reached (…). Figure 5A The durations of t1 and vibration segment S are greatly shortened, and multiple DC balance and vibration segments can be used to apply (i) a zero voltage period of duration t2; (ii) a period of high positive drive voltage VH1 of duration t3; (iii) a zero voltage period of duration t4 that is much longer than t3; and (iv) repeating (ii) and (iii) multiple times, typically 4-8 times.

[0082] Figure 5B The following diagram illustrates the implementation. Figure 3B The waveform that produces the yellow optical state (i.e., the color of the second particle) is transformed. As already noted, in principle, yellow can be produced by applying alternating pulses of a high negative potential difference (e.g., -15V) and no voltage (0V) to the pixel electrode 22a for a sufficiently long period of time. However, to ensure a pure yellow, a more complex waveform is preferred, such as... Figure 5B As shown. In conjunction with already referenced Figure 5A After the DC equilibrium part and the vibration part S, which are described as having essentially the same duration t1, Figure 5B The waveform includes a zero-voltage period of duration t5, followed by (i) a short period of high negative potential difference VH2 lasting duration t6; (ii) a zero-voltage period of duration t7; and (iii) a period of low positive potential difference VL1 lasting duration t8, which is longer than t6. Typically, the amplitude of VL1 is about half that of VH2, the length of t7 is comparable to that of t6, and t8 is about ten times the length of t6. For example, each of t6 and t7 can be 50 milliseconds, while t8 can be 500 milliseconds. Steps (i), (ii), and (iii) are then repeated several times, as follows: Figure 5BAs indicated by “[X m]”; typically, these steps can be repeated 4-6 times. After these repetitions, (iv) a high negative potential difference VH2 is applied for a time period t9, which is longer than t6, and then (v) a low positive potential difference VL3, which is lower than VL1 and typically about one-third of VH1, is applied for a time period t10, which is shorter than t8. Then steps (iv) and (v) are repeated as follows. Figure 5B As shown in “[Xn]”; typically, these steps can be repeated 2-3 times. Figure 5B The final part of the waveform includes the application of a high negative potential difference VH2 for a time period t11 (longer than t9), a zero-voltage time period for a duration t12, and a second application of the high negative potential difference VH2 for a time period t11. It is easy to see that the number of times VH2 is applied and the duration t11 in this part of the waveform can be adjusted empirically.

[0083] Figure 5C The following diagram illustrates the implementation. Figure 3C The transition produces a waveform of red optical state (i.e., the color of the second particle). Figure 5C The waveform shown is Figure 5B The first part of the waveform shown is very similar; in comparison with the reference... Figure 5A After the DC equilibrium part and the vibration part S, which are described as having essentially the same duration t1, Figure 5C The waveform includes a zero-voltage period of duration t13, followed by (i) a short period of high negative potential difference VH2 lasting t14; (ii) a zero-voltage period of duration t15; and a period of low positive potential difference VL1 lasting t16, which is longer than t14. Typically, the amplitude of VL1 is about half that of VH2, the length of t15 is comparable to that of t14, and t16 is about ten times the length of t14. For example, each of t6 and t7 can be 50 milliseconds, while t8 can be 500 milliseconds. Steps (i), (ii), and (iii) are then repeated several times, as follows: Figure 5C As shown; typically, these steps can be repeated 6-10 times. The waveform terminates by transitioning from the final application of VL1 to 0V to ensure a good red color. It is evident that the number of applications of VH2 and VL1 in this waveform, as well as the durations t14 and t16, can be adjusted empirically.

[0084] Figure 5D The following diagram illustrates the implementation. Figure 3D The waveform is transformed to produce a white optical state (i.e., the color of the fourth particle). Unsurprisingly, Figure 5D The first part of the waveform shown is... Figure 5C The "red" waveform shown is very similar, but the polarity has changed compared to the reference waveform. Figure 5AFollowing the essentially identical duration t1' of the DC equilibrium portion (in this case, the DC equilibrium portion is highly positive) and the vibration portion S, Figure 5D The waveform includes (i) a short period of high positive potential difference VH1 with a duration of t17 (note that in this case, there is no zero voltage period between the oscillating part S and the application of the high driving potential difference); (ii) a zero voltage period with a duration of t18; and a period of low negative potential difference VL2 with a duration longer than t17, t19. Typically, the amplitude of VL2 is about half that of VH1, the length of t18 is comparable to that of t17, and t19 is about ten times the length of t17. For example, each of t6 and t7 can be 50 milliseconds, while t8 can be 500 milliseconds. Then steps (i), (ii), and (iii) are repeated several times, as follows. Figure 5D As shown; typically, these steps can be repeated 6-10 times. However, to ensure pure white, it has been found advantageous to repeat steps (i), (ii), and (iii) followed by (iv) a period of zero potential difference for duration t20; (v) applying a low negative potential difference VL2 for duration t21; and repeating steps (iv) and (v). Typically, steps (iv) and (v) will be repeated 6-10 times, t20 will be comparable to t18, and t21 will be shorter than t19. It is evident that the number of times VH1 and VL2 are applied in this waveform, as well as the durations t17, t18, t19, t20, and t21, can be adjusted empirically.

[0085] Figure 5E The following diagram illustrates the implementation. Figure 3E The transition produces a waveform that generates a blue optical state (i.e., the color of the first particle); this waveform is an example of the second driving method of the present invention. Unsurprisingly, Figure 5E The first part of the waveform shown is... Figure 5D The “white” waveform shown is the same. However, after repeating steps (iv) and (v) discussed in the previous paragraph, Figure 5E The waveform continues with (vi) the application of a high positive potential difference VH1 for a time period t22 shorter than t17; (vii) the application of a zero potential difference for a time period t23 shorter than t18; (viii) the application of a low negative potential difference VL4 with an amplitude smaller than VL2 for a time period t24 shorter than t19 or t21; and the repetition of steps (vi)-(viii), but ending with the repetition of step (vi) without following the repetition of step (viii), i.e., with a final positive drive pulse, as referenced above. Figure 3E As described above. Typically, the amplitude of VL4 is approximately 75% of that of VL2, and steps (vi)-(viii) can usually be repeated 10-20 times. Obviously, the number of times VH1 and VL4 are applied in this waveform, as well as the durations t22, t23, and t24, can be adjusted empirically.

[0086] at last, Figure 5F The following diagram illustrates the implementation. Figure 3F The transition shown produces a waveform in an orange optical state; this waveform is an example of the third driving method of the present invention. Figure 5F The waveform shown is Figure 5C The “red” waveform shown is the same, except that a final short, low negative potential difference pulse SP is added, whose impulse is insufficient to drive the electrophoretic medium from the red optical state (R) to the yellow optical state (Y) (see [link]). Figure 3B The amplitude and duration of the pulse SP can vary widely, and the optical combination of amplitude and duration can be determined empirically.

[0087] Figure 1 The four-particle electrophoresis medium shown was formulated using the following: Kremer 45030 as a partially translucent blue pigment, rutile titanium dioxide white pigment, and light-reflecting 1254 DPP Red 254 (available from DCL Corporation) and Novoperm Yellow HR 70-EDS (available from Clariant Corporation, Holden MA) from Isopar E, with added charge control pigments. Even using an unoptimized waveform, the following five colors were produced:

[0088] surface

[0089] color L* a* b* White 63 -2.4 2.6 blue 30.2 4.2 -35.4 red 26.8 37.9 24.6 yellow 58.8 4.6 54.2 black 13.1 7.2 -8.5

[0090] Figure 1 , 3A The electrophoretic media shown in -3F and 5A-5F include type I partially transparent highly positive blue particles, type II highly reflective highly negative yellow particles, type III low-reflective red particles, and type IV low-negative white particles. However, other colors can be produced by changing the partially transparent highly positive particles to red and the low-reflective low-positive particles to blue; in particular, this combination allows the electrophoretic media to display black, white, red, blue, and green, as follows: Figures 6A-6F As shown. Therefore, this system can display black, white, and the three normal additive primary colors; additional colors can be generated through area modulation (dithering).

[0091] Figure 6A It shows something similar to Figure 3A The transition shown begins in a fully mixed state (M). In the final state (K), the red translucent particles are adjacent to the common electrode 21, and the blue reflective particles are adjacent to them below (as shown). Figure 6A (as shown), therefore, although with Figure 3A In contrast, the positions of the red and blue particles are reversed, still generating a black optical state.

[0092] Figure 6B It shows something similar to Figure 3B The transformation shown in the diagram. The yellow state reappears because the yellow particles adjacent to the common electrode mask the white, red, and blue particles, thus... Figure 3B compared to, Figure 6B The reversal of the positions of the red and blue particles did not affect the optical state.

[0093] Figure 6C It shows something similar to Figure 3C The transformation shown. With Figure 3C The same as in the middle, Figure 6C The transition brings the low-positive particles closer to the common electrode, and since these low-positive particles are now reflective blue particles, a blue optical state is produced, rather than... Figure 3C The red optical state.

[0094] Figure 6D It shows something similar to Figure 3D The transformation shown in the diagram. A white state is re-generated because the white particles adjacent to the common electrode mask the yellow, red, and blue particles, thus... Figure 3D compared to, Figure 6D The reversal of the positions of the red and blue particles did not affect the optical state.

[0095] Figure 6E It shows something similar to Figure 3E The transformation shown. With Figure 3E The same as in the middle, Figure 6E The transition brings the mixture of highly positive particles and white particles close to the common electrode, and since these highly positive particles are now transparent red particles, a red optical state (R) is generated instead of... Figure 3E The blue optical state.

[0096] at last, Figure 6F It shows something similar to Figure 3F The transition is shown in the diagram. The initial state is one where low-positive particles are located near the common electrode. Figure 6F The medium is in the blue optical state (B). Therefore, the final state has a mixture of low positive blue particles and high negative yellow particles adjacent to the common electrode, thus exhibiting the green optical state (G).

[0097] The above reference Figures 5A-5F The description is for implementation respectively Figures 3A-3F Each waveform of the transformation can also be used to achieve the transformation separately. Figures 6A-6F The corresponding transformation.

[0098] Figures 7A-7F It is similar to Figures 3A-3FThe diagram shows a schematic cross-section, but illustrates the various optical transitions that the five-particle display device of the present invention can undergo. Figures 7A-7F The electrophoretic medium shown is Figures 3A-3F The electrophoretic media shown are generally similar, and therefore include yellow particles (Y) with a high negative charge, white particles (W) with a low negative charge, red particles (R) with a low positive charge, and transparent blue particles (B) with a positive charge, whose electromotive force is greater than that of the red particles. However, the blue particles are only the intermediate positive particles because... Figures 7A-7F The electrophoretic medium shown also includes green particles (G) with a high positive charge, whose electromotive force is greater than that of the blue particles (B). The yellow, white, and green particles are all light-reflective.

[0099] Figure 7A The transition shown begins from a fully mixed state, denoted as "(M)," and is generated by applying vibrational pulses as described below. This transition is similar to... Figure 3A The transition shown involves applying alternating pulses of high positive potential difference (e.g., +15V) and no potential difference (0V) to pixel electrode 22a for a sufficiently long period, thereby driving green (G), blue (B), and red (R) particles toward the common electrode (21) or the viewing side, and driving yellow (Y) and white (W) particles toward the pixel electrode 22a side. Since green particles are more charged than blue and red particles, green particles are positioned close to the common electrode, and blue and red particles are positioned close to them below (e.g., ...). Figure 7A As shown), this causes the pixel to appear green, in Figure 7A The value is represented as "(G)"; blue, red, white, and yellow particles are masked by reflective red particles, without affecting the displayed color.

[0100] Figure 7B The transformation shown is Figure 3B The transitions shown are exactly the same; when alternating pulses of a high negative potential difference (e.g., -15V) and no voltage (0V) are applied to the pixel electrode 22a of a pixel in the fully mixed state (M), yellow and white particles are driven toward the common electrode side, while red, blue, and green particles are driven toward the pixel electrode side. Since yellow particles are more charged than white particles, reflective yellow particles are located close to the common electrode, causing the pixel to appear yellow. Figure 7B The color is represented as “(Y)”; white, red, blue and green particles are masked by reflective yellow particles, without affecting the displayed color.

[0101] Figure 7C The transformation shown is from Figure 7BThe yellow state (Y) is shown. When alternating pulses of high negative potential difference (e.g., -15V) and low positive potential difference (e.g., +8V) are applied to pixel electrode 22a for a sufficiently long period of time (the low positive pulse is much longer than the high negative pulse), red (R) particles are driven toward the common electrode 21 side, while white particles (W) are driven toward the pixel electrode 22a side. The oscillating electric field causes the highly charged green and yellow particles, and the moderately charged blue particles, to repeatedly pass through the middle of the electrophoretic layer thickness. The strong electro-attraction between these charged positive and negative particles greatly slows down their movement and tends to keep them in the middle of the electrophoretic layer thickness. However, the electric field generated by the low positive pulse is sufficient to separate the low-charged white and red particles, thus allowing the low positive red particles (R) to move all the way to the common electrode 21 side and the low negative white particles to move to the pixel electrode 22a side. As a result, reflective red particles are close to the common electrode, thus making the pixel appear red. Figure 7C The symbol is represented as "(R)"; white, yellow, blue and green particles are masked by reflective red particles without affecting the displayed color.

[0102] Figure 7D The transformation shown is from Figure 7A The green state (G) is shown. When alternating pulses of high positive potential difference (e.g., +15V) and low negative potential difference (e.g., -8V) are applied to pixel electrode 22a for a sufficiently long period of time (the low negative pulse is much longer than the high positive pulse), red (R) particles are driven toward the pixel electrode 22a side, and white particles (W) are driven toward the common electrode 21 side. Figure 7C The transition shown is that the oscillating electric field keeps the highly charged green and yellow particles and the moderately charged blue particles together in the middle of the electrophoretic layer thickness. However, the electric field generated by the low-negative pulses is sufficient to separate the low-charge white and red particles, allowing the low-positive red particles (R) to move all the way to the pixel electrode 22a side and the low-negative white particles to move to the common electrode 21 side. As a result, the white particles are close to the common electrode, causing the pixel to appear white. Figure 7D The white particle is represented as "(W)"; red, yellow, blue and green particles are masked by white particles, which does not affect the displayed color.

[0103] Figure 7E The transformation shown is from Figure 7DThe white state (W) is shown. When alternating pulses of high positive potential difference (e.g., +15V) and intermediate negative potential difference (e.g., -10V) are applied to pixel electrode 22a for a sufficiently long period of time (the negative pulse is much longer than the positive pulse), blue particles "escape" from the green / yellow / blue particle aggregate and gradually migrate towards the common electrode 21. White particles similarly migrate in the opposite direction, causing a mixture of blue and white particles to form near the common electrode, which can be seen by observing the surface. Figure 7E The blue color is represented by "(B)". Red particles migrate away from the pixel electrodes; Figure 7E The image shows red particles mixed with yellow and green particles, but whether such a mixture forms, or whether the red particles remain in a separate layer adjacent to the pixel electrode, is irrelevant to the displayed color, because blue and white particles near the common electrode will mask the yellow, green, and red particles. The above regarding... Figure 3E The comments regarding blue saturation, and the question of whether blue and white particles are mixed or in discrete layers, also apply. Figure 7E The blue state shown in the image.

[0104] at last, Figure 7F The transformation shown is from Figure 7A The green state (G) is shown. Applying an appropriate waveform (discussed below) causes the positively charged green, blue, and red particles to move away from the common electrode 21. However, because the green particles carry a stronger charge than the blue and red particles, they move faster than the blue and red particles, thus causing the blue and red particles adjacent to the common electrode to... Figure 7F The discrete layer shown may be used as a hybrid layer. In either case, since it has already been referenced... Figure 3A The reasons discussed led to the emergence of Figure 7F The black state is represented by "(K)". Since red and blue particles mask green, yellow, and white particles, the exact positions of the green, yellow, and white particles do not affect the visible color. However, because both white and yellow particles move away from pixel electrode 22a, and yellow particles move faster than white particles, the most likely state is... Figure 7F As shown in the diagram, green and yellow particles are clustered in the middle of the electrophoretic layer, while white particles are adjacent to the pixel electrodes.

[0105] Figure 7A and 7B The transformations shown can be used separately. Figure 5A and 5B The waveforms shown are used to achieve this. (Understandably, some optimization of these waveforms may be necessary, depending on the exact electrophoretic mobility of the particles used, their charge, and similar factors.) Similarly, it can be achieved using... Figure 5C The waveform shown is implemented as follows from the mixed state (M) to Figure 7BThe yellow state (Y) is shown, then... Figure 7C The overall transition to the red state (R) is shown. Additionally, it can be used... Figure 5D The waveform shown achieves the transition from the mixed state (M) to... Figure 7A The green state (G) is shown, then... Figure 7D The overall transformation of the white state (W) shown.

[0106] Figure 7E The white-to-blue transition shown can be used Figure 8A The waveform shown is used to achieve this. This waveform consists of a short, high positive pulse of voltage VH1 for duration t25, followed by a zero-voltage period for duration t26 and a period of intermediate negative voltage VLI for duration t27, where t27 is significantly longer than t25. This sequence is then repeated several times. Figure 8A Five repetitions are shown, but the number of repetitions can vary widely. It can be understood that in order to generate the blue state (B) from the mixed state (M), an application should be made... Figure 5D The waveform shown, then... Figure 8A The waveform shown.

[0107] Figure 7F The green-to-black transition shown can in many cases be influenced by a single short high-voltage negative pulse (or a series of short high-voltage negative pulses separated by zero-voltage periods), sufficient to move green particles below the blue and red particles, thus leaving a mixture of red and blue particles near the common electrode and producing the desired black color. Therefore, it is possible to use... Figure 3A The waveform, followed by one or more high-voltage negative pulses, from Figure 7A The mixed state (M) shown produces black. However, in some cases, depending on the precise electrophoretic mobility of the green, blue, and red particles, using one or more such high-voltage negative pulses may cause the blue particles to be on average farther from the common electrode than the red particles, resulting in a color ranging from deep red to reddish-black. If this problem occurs, it can be addressed using... Figure 8B The waveform is used to achieve Figure 7F The transformation from green to black.

[0108] Figure 8B The waveform begins with a brief high negative pulse of duration t28, followed by a zero-voltage period of duration t29, where t29 is longer than t28. This sequence of high negative pulses and zero voltage is repeated, followed by a third high negative pulse of duration t28; a larger or smaller number of pulses can, of course, be used if desired. By comparison... Figure 8B and Figure 5AAs can be seen, the function of the three negative pulses is to reverse the driving part of the green particles to the common electrode and drive the yellow particles to the pixel electrode, thereby bringing the green and yellow particles closer to the middle of the electrophoretic layer, where they can gather, as mentioned earlier. Figure 8B The second part of the waveform shown includes three intermediate voltage positive pulses, each with a duration of t30, separated by a zero-voltage period of duration t31, where t30 is greater than t28. The durations t28 and t30, as well as the applied driving voltage, are chosen such that the impulse applied by the positive pulses is substantially equal in amplitude but opposite in polarity to the impulse applied by the negative pulses. The positive pulses do not substantially cause a change in the position of the yellow and green particles because the intermediate voltage used is insufficient to break down the green / yellow aggregates; however, these positive pulses do substantially restore the red, blue, and white particles to their positions as applied. Figure 8B The waveforms that they occupied before the waveforms, thus producing... Figure 7F The final particle position is shown in (K).

[0109] As can be seen from the above, the present invention can provide a four-particle electrophoresis medium that can produce at least five, and in some cases, six, useful colors using only four different types of particles. The five-particle electrophoresis medium of the present invention can produce at least six useful colors. It should be noted that in practice (e.g.) Figure 7A The five-particle system shown produces a green ratio Figure 6F The four-particle system shown produces a more consistent green because the former is the natural color of a pigment particle, while the latter can vary depending on the exact location of the blue and yellow particles, which may be difficult to maintain precisely over the lifespan of the display.

[0110] The electrophoresis medium and apparatus of the present invention can be designed using any particles, fluids, encapsulation materials and electrophoresis apparatus described in the prior art, such as those described below:

[0111] (a) Electrophoretic particles, fluids, and fluid additives; U.S. Patent Nos. 7,002,728 and 7,679,814;

[0112] (b) Encapsulation, adhesives, and encapsulation processes; U.S. Patent Nos. 6,922,276 and 7,411,719;

[0113] (c) Microunit structures, wall materials, and methods of forming microunits; U.S. Patent Nos. 7,072,095 and 9,279,906;

[0114] (d) Methods for filling and sealing microcells; see, for example, U.S. Patent Nos. 7,144,942 and 7,715,088;

[0115] (e) Thin films and subassemblies comprising electro-optic materials; see, for example, U.S. Patent Nos. 6,825,829; 6,982,178; 7,112,114; 7,158,282; 7,236,292; 7,443,571; 7,513,813; 7,561,324; 7,636,191; 7,649,666; 7,728,811; 7,729,039; 7,791,782; 7,826,129; 7,839,564; 7,843,621; 7,843,624; 8,034,209; 8,068,272; 8,077,381; 8,177,942; 8,390,301; 8,482,835; 8,786,929; 8,830,553; 8,854,721; 9,075,280; 9,238,340; 9,470,950; 9,554,495; 9,563,099; 9,733,540; 9,778,536; 9,835,925; 10,444,591; and 10,466,564; and U.S. Patent Application Publication Nos. 2007 / 0237962; 2009 / 0168067; and 2011 / 0164301;

[0116] (f) Backplanes, adhesive layers and other auxiliary layers for use in displays, and methods thereof; see, for example, U.S. Patent Nos. 7,116,318 and 7,535,624;

[0117] (g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 6,017,584; 6,545,797; 6,664,944; 6,788,452; 6,864,875; 6,914,714; 6,972,893; 7,038,656; 7,038,670; 7,046,228; 7,052,571; 7,075,502; 7,167,155; 7,385,751; 7,492,505; 7,667,684; 7,684,108; 7,791,789; 7,800,813; 7,821,702; 7,839,564; 7,910,175; 7,952,790; 7,956,841; 7,982,941; 8,040,594; 8,054,526; 8,098,418; 8,159,636; 8,213,076; 8,363,299; 8,422,116; 8,441,714; 8,441,716; 8,466,852; 8,503,063; 8,576,470; 8,576,475; 8,593,721; 8,605,354; 8,649,084; 8,670,174; 8,704,756; 8,717,664; 8,786,935; 8,797,634; 8,810,899; 8,830,559; 8,873,129; 8,902,153; 8,902,491; 8,917,439; 8,964,282; 9,013,783; 9,116,412; 9,146,439; 9,164,207; 9,170,467; 9,170,468; 9,182,646; 9,195,111; 9,199,441; 9,268,191; 9,285,649; 9,293,511; 9,341,916; 9,360,733; 9,361,836; 9,383,623; 9,423,666; 9,436,056; 9,459,510; 9,513,527; 9,541,814; 9,552,780; 9,640,119; 9,646,547; 9,671,668; 9,697,778; 9,726,959; 9,740,076; 9,759,981; 9,761,181; 9,778,538; 9,779,670; 9,779,671; 9,812,073; 9,829,764;9,921,451; 9,922,603; 9,989,829; 10,032,419; 10,036,929;10,036,931; 10,332,435; 10,339,876; 10,353,266; 10,366,647; 10,372,010; 10,380,931; 10,380,955; 10,431,168; 10,444,592; 10,467,984; 10,475,399; 10,509,293; and 10,514,583; 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; 2015 / 0103394; 2015 / 0118390; 2015 / 0124345; 2015 / 0268531; 2015 / 0301246; 2016 / 0026062; 2016 / 0048054; and 2016 / 0116818;

[0118] (h) A method for driving a display; see, for example, U.S. Patent Nos. 7,012,600 and 7,453,445; and

[0119] (i) Applications of displays; see, for example, U.S. Patent Nos. 7,312,784 and 8,009,348.

[0120] Electrophoretic displays typically comprise an electrophoretic material layer and at least two other layers disposed on opposite sides of the electrophoretic material, one of which is an electrode layer. In most such displays, both layers are electrode layers, and one or both electrode layers are patterned to define pixels of the display. For example, one electrode layer may be patterned as elongated row electrodes, while the other electrode layer may be patterned as elongated column electrodes extending perpendicularly to the row electrodes, with pixels defined by the intersections of the row and column electrodes. Alternatively, and more generally, one electrode layer has the form of a single continuous electrode, while the other electrode layer is patterned as a matrix of pixel electrodes, each pixel electrode defining one pixel of the display.

[0121] The manufacture of three-layer electrophoretic displays typically involves at least one lamination operation. For example, several of the aforementioned patents and applications describe a process for manufacturing encapsulated electrophoretic displays, wherein an encapsulated electrophoretic medium, comprising a capsule in an adhesive, is coated onto a flexible substrate containing an indium tin oxide (ITO) or similar conductive coating (serving as an electrode of the final display) on a plastic film; the capsule / adhesive coating is then dried to form a coherent layer of electrophoretic medium firmly adhered to the substrate. Separately, a backplate comprising a pixel electrode array and a suitably arranged conductor for connecting the pixel electrodes to driving circuitry is prepared. To form the final display, the substrate having the capsule / adhesive layer thereon is laminated to the backplate using a lamination adhesive. In a preferred form of this process, the backplate itself is flexible and is prepared by printing pixel electrodes and conductors onto a plastic film or other flexible substrate. An obvious lamination technique for mass-producing displays using this process is roll lamination using a lamination adhesive.

[0122] As discussed in the aforementioned U.S. Patent No. 6,982,178 (see column 3, lines 63 through 5, lines 46), many of the components used in electrophoretic displays, and the methods for manufacturing such displays, are derived from the technology used in liquid crystal displays (LCDs). For example, an electrophoretic display may use an active matrix backplane comprising an array of transistors or diodes and corresponding arrays of pixel electrodes, and a “continuous” front electrode on a transparent substrate (in the sense that the electrode extends to multiple pixels, and generally the entire display), components substantially identical to those in an LCD. However, the methods used to assemble LCDs cannot be used for packaged electrophoretic displays. LCDs are typically assembled by forming a backplane and front electrodes on separate glass substrates, then bonding these components together, leaving a hole between them, placing the resulting assembly under vacuum, and immersing the assembly in a liquid crystal bath so that liquid crystal flows through the hole between the backplane and front electrodes. Finally, after the liquid crystal is in place, the hole is sealed to provide the final display.

[0123] This LCD assembly process cannot be easily transferred to encapsulated electrophoretic displays. Because the electrophoretic material is typically solid (i.e., has a solid outer surface), it must exist between the backplate and the front electrode before the backplate and front electrode are attached to each other. Furthermore, compared to liquid crystal material simply placed between the front electrode and the backplate without adhering to either, the solid electro-optic dielectric usually needs to be attached to both. In most cases, the solid electro-optic dielectric is formed on the front electrode, as this is generally easier than forming the dielectric on the backplate containing the circuitry. The front electrode / electro-optic dielectric combination is then typically laminated to the backplate by covering the entire surface of the electro-optic dielectric with an adhesive and laminating under heat, pressure, and possibly vacuum. Therefore, most prior art methods for the final lamination of solid electrophoretic displays are essentially batch methods, where the electro-optic dielectric, lamination adhesive, and backplate are (typically) placed together immediately before final assembly, and a method more suitable for mass production is desired.

[0124] The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling a solid-state electro-optic display (including an encapsulated electrophoretic display), which is well-suited for mass production. Essentially, the patent describes a so-called “front-plane laminate” (“FPL”) comprising, in sequence, a light-transmitting conductive layer, a solid electro-optic dielectric layer electrically in contact with the conductive layer, an adhesive layer, and a release sheet. Typically, the light-transmitting conductive layer is carried on a light-transmitting substrate, preferably flexible, in such a sense that the substrate can be manually wound around (e.g.) a drum with a diameter of 10 inches (254 mm) without permanent deformation. The term “light-transmitting” is used in this patent and herein refers to a layer that transmits sufficient light to allow an observer to see through it to observe changes in the display state of the electro-optic dielectric, typically through the conductive layer and adjacent substrates (if present); in cases where the electro-optic dielectric displays changes in reflectivity at invisible wavelengths, the term “light-transmitting” should, of course, be interpreted as relating to the transmission of the relevant invisible wavelengths. The substrate is typically a polymer film and will generally have a thickness ranging from about 1 to about 25 mils (25 to 634 micrometers), preferably from about 2 to about 10 mils (51 to 254 micrometers). The conductive layer is conveniently a thin metal or metal oxide layer, such as aluminum or ITO, or may be a conductive polymer. Polyethylene terephthalate (PET) films coated with aluminum or ITO are commercially available, for example, "Aluminum-coated Mylar" ("Mylar" is a registered trademark) from DuPont in Wilmington, Delaware, and such commercial materials perform well in front-plane laminates.

[0125] Assembly of an electro-optic display using this front-plane laminate can be achieved by removing the release sheet from the front-plane laminate and bringing the adhesive layer into contact with the backplate while ensuring effective adhesion of the adhesive layer to the backplate, thereby securing the adhesive layer, electro-optic dielectric layer, and conductive layer to the backplate. This process is well-suited for mass production because the front-plane laminate can typically be mass-produced using roll-to-roll coating technology and then cut into blocks of any size for a specific backplate.

[0126] U.S. Patent No. 7,561,324 describes a so-called "dual-release sheet," which is essentially a simplified version of the front-plane laminate of the aforementioned U.S. Patent No. 6,982,178. One form of dual-release sheet includes a solid electrophoretic dielectric layer sandwiched between two adhesive layers, one or both of which are covered by the release sheet. Another form of dual-release sheet includes a solid electrophoretic dielectric layer sandwiched between two release sheets. Both forms of dual-release films are intended for use in processes substantially similar to those described for assembling electro-optic displays from front-plane laminates, but involve two separate laminations; typically, in the first lamination, the dual-release sheet is laminated to the front electrode to form the front sub-assembly, and then in the second lamination, the front sub-assembly is laminated to the backplane to form the final display, but the order of these two laminations can be reversed if desired.

[0127] U.S. Patent No. 7,839,564 describes a so-called "inverted front-plane laminate," a variation of the front-plane laminate described in U.S. Patent No. 6,982,178. This inverted front-plane laminate sequentially comprises at least one of a light-transmitting protective layer and a light-transmitting conductive layer, an adhesive layer, a solid electrophoretic dielectric layer, and a release sheet. This inverted front-plane laminate is used to form an electro-optic display having a laminated adhesive layer between the electrophoretic layer and the front electrode or front substrate; a second layer, typically a thin adhesive layer, may or may not be present between the electrophoretic layer and the backplate. This electro-optic display can combine good resolution with good low-temperature performance.

Claims

1. A method for driving an electrophoretic display, the electrophoretic display comprising an electrophoretic medium having an observation surface on one side and a second surface on the opposite side, the electrophoretic display device further comprising a voltage control device for applying an electric field through the electrophoretic medium layer; the electrophoretic medium comprising a fluid and particles of a first type, a second type, a third type, and a fourth type dispersed in the fluid, the first type, the second type, the third type, and the fourth type particles being partially translucent red, light-reflecting yellow, light-reflecting blue, and white, respectively; the first and third type particles having a single polarity of charge, while the second and fourth type particles having opposite polarities of charge; the first type particles having a greater electromotive force or electrophoretic mobility than the third type particles, and the second type particles having a greater electromotive force or electrophoretic mobility than the fourth type particles, the method comprising: (i) Applying a DC balanced pulse having a first driving voltage and a first polarity to the electrophoretic medium; (ii) After step (i), a vibrational voltage pulse is applied to the electrophoretic medium to achieve a mixed color state in which all four types of particles are randomly distributed in the fluid; (iii) After step (ii), a zero voltage is applied to the electrophoretic medium and maintained for a first time period; (iv) After step (iii), a second driving voltage is applied to the electrophoretic medium and sustained for a second time period, the second driving voltage having the same amplitude as the first driving voltage and a polarity opposite to the first polarity; (v) After step (iv), a zero voltage is applied to the electrophoretic medium for a third time period, the third time period being longer than the second time period; (vi) Repeat steps (iv) and (v) multiple times until the processed black is visible on the observed surface.

2. The method according to claim 1, wherein, The "multiple times" includes at least four times.

3. A method for driving an electrophoretic display, the electrophoretic display comprising an electrophoretic medium having an observation surface on one side and a second surface on the opposite side, the electrophoretic display further comprising a voltage control device for applying an electric field through the electrophoretic medium layer; the electrophoretic medium comprising a fluid and particles of a first type, a second type, a third type, and a fourth type dispersed in the fluid, the first type, the second type, the third type, and the fourth type particles being partially translucent red, light-reflecting yellow, light-reflecting blue, and white, respectively; the first and third type particles having a single polarity of charge, while the second and fourth type particles having opposite polarities of charge; the first type particles having a larger electromotive force or electrophoretic mobility than the third type particles, and the second type particles having a larger electromotive force or electrophoretic mobility than the fourth type particles, the method comprising: (i) Drive the electrophoretic medium to display white on the observation surface; (ii) After step (i) is completed, a first driving voltage is applied to the electrophoretic medium and sustained for a first time period, the first driving voltage having a polarity that drives the first and third types of particles toward the observation surface; (iii) After step (ii) is completed, a zero voltage is applied to the electrophoretic medium and maintained for a second time period; (iv) After step (iii) is completed, a second driving voltage is applied to the electrophoretic medium and sustained for a third time period, wherein the polarity of the second driving voltage is opposite to that of the first driving voltage and the amplitude is smaller than that of the first driving voltage, and the third time period is longer than the first time period; (v) Repeat steps (ii) to (iv) multiple times until red appears on the observation surface.

4. The method according to claim 3, wherein, The "multiple times" includes at least four times.

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