Color electrophoretic layer comprising microcapsules with non-ionic polymeric walls

Abstract

A capsule comprising a capsule wall and an electrophoretic fluid encapsulated by the capsule wall. The capsule wall comprises a crosslinked non-ionic, water-soluble or water-dispersible polymer. The electrophoretic fluid comprises a suspending fluid, first pigment particles, second pigment particles, and third pigment particles. In some embodiments, the electrophoretic fluid comprises fourth electrophoretic particles. The first, second, and third particles are charged, suspended in the suspending fluid, and capable of moving through the suspending fluid when an electric field is applied to the capsule.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 952,534, filed December 23, 2019. All references, patents, and patent applications disclosed herein are incorporated herein by reference in their entirety.

[0003] background

[0004] Traditional electrophoretic displays based on microencapsulated pigments, such as those found in most e-readers, use a gelatin-gum aggregate to form the microcapsule walls. This material has been shown to provide excellent performance for black and white displays, and these capsules are relatively easy to manufacture. More sophisticated three- and four-color electrophoretic systems have been developed in which pigments are encapsulated in micropores rather than microcapsules. (Methods for forming, filling, and sealing such micropores are described in numerous patents and patent applications held by E Ink.) However, for large-area display applications, a microcapsule architecture may be preferred because, in some embodiments, the maximum size of the imprinted micropore region may be limited by the diameter of the imprinting cylinder.

[0005] It would be useful to include microcapsules containing three or more pigments in the device, so that with only minor adjustments to the addressing waveform, the same electrophoretic fluid (multiple fluids) would produce optical states similar to those obtained in microporous chambers or liquid test orifices (e.g., test pixels). This is typically not possible using gelatin / arabic capsule walls.

[0006] Encapsulation has a long and rich history in this area, with numerous methods and polymers proposed as materials for electrophoresis capsules. For example, U.S. Patent Application Publication No. 2006 / 0245038 suggests a large number of possible substances, including gelatin, polyvinyl alcohol, polyvinyl acetate, and cellulose derivatives, as materials for manufacturing the capsule wall via coagulation. However, no guidance is provided regarding the potential impact of the capsule wall material on the function of the enclosed electrophoretic fluid.

[0007] Overview

[0008] In a first aspect, a capsule for an electrophoretic medium is provided. The capsule includes a capsule wall and an electrophoretic fluid encapsulated by the capsule wall. Specifically, the capsule includes a capsule wall comprising a water-soluble (or water-dispersible) and cross-linked nonionic polymer, and the electrophoretic fluid comprises a suspension solvent, first pigment particles, second pigment particles, and third pigment particles, wherein the first, second, and third particles are of different colors, charged, suspended in the suspension fluid, and capable of moving through the suspension fluid when an electric field is applied to the capsule. In some embodiments, the nonionic polymer is a polyol. In some embodiments, the polyol is polyvinyl alcohol. In some embodiments, the capsule wall comprises a solidified coagulated layer formed of a nonionic polymer and polyvinyl lactone, optionally polyvinylpyrrolidone. In some embodiments, the capsule wall is cross-linked by a reaction with a dialdehyde, optionally glutaraldehyde. In some embodiments, the suspension solvent comprises a hydrocarbon, such as a mixture of hydrocarbons, such as those available from Sigma-Aldrich. E. In some embodiments, one or more of the pigment particles are reflective. In some embodiments, one or more of the pigment particles are absorbent. In some embodiments, the electrophoretic fluid further comprises a fourth pigment particle. In some embodiments, the electrophoretic fluid comprises white pigment, yellow pigment, magenta pigment, and cyan pigment. In some embodiments, the electrophoretic fluid comprises white pigment, black pigment, yellow pigment, and red pigment. In some embodiments, the electrophoretic fluid comprises black pigment, red pigment, yellow pigment, and blue pigment. In some embodiments, the capsule of the present invention may be contained in an electrophoretic medium that further comprises a binder surrounding the capsule. In some embodiments, the capsule has an average diameter of 15 μm to 50 μm, and less than one-third of the capsules (by number) are less than 15 μm or greater than 50 μm. This electrophoretic medium may incorporate into an electrophoretic display comprising at least one electrode adjacent to the electrophoretic medium and arranged to apply an electric field to the electrophoretic medium. The electrophoretic display may be rectangular and have a diagonal dimension greater than 30 cm, for example, greater than 50 cm. The electrophoretic display may additionally include a second electrode or electrode layer, which may include an array of pixel electrodes controlled by thin-film transistors. In some embodiments, one or more of the electrodes may be light-transmitting.

[0009] In a second aspect, a method for manufacturing the capsule of the present invention is provided. The method includes providing a polymer solution comprising a nonionic, water-soluble, or water-dispersible starting polymer in an aqueous solvent; providing an electrophoretic fluid comprising a suspending solvent and pigment particles; mixing the polymer solution and the electrophoretic fluid to generate a reaction mixture; heating the reaction mixture to a temperature above the minimum critical solution temperature of the polymer solution to form an oil-in-water emulsion comprising the electrophoretic fluid; adding a crosslinking agent to the oil-in-water emulsion to form a cured mixture; and heating the cured mixture to form a capsule encapsulating the electrophoretic medium. In some embodiments, the polymer solution comprises polyvinyl alcohol. In some embodiments, the polymer solution comprises a copolymer of vinyl acetate. In some embodiments, the method further includes adding a second nonionic, water-soluble, or water-dispersible starting polymer to the polymer solution. In some embodiments, the second nonionic polymer is polyvinylpyrrolidone. In some embodiments, the crosslinking agent is glutaraldehyde. In some embodiments, the method further includes adding a coagulation inducing agent to the polymer solution. In some embodiments, the coagulation inducing agent is a water-soluble (or water-dispersible) salt. In some embodiments, the salt is a sulfate, such as sodium sulfate. Brief description of the attached diagram

[0011] Figure 1A This is a schematic diagram of a typical packaged electrophoretic display. Figure 1B This is a schematic diagram of an exemplary packaged electrophoretic display containing three different types of charged pigment particles.

[0012] Figure 2 A schematic diagram of a thin-film transistor (TFT) array for controlling pixel electrodes and associated scan (gate) and data (source) drivers.

[0013] Figure 3 This is a schematic flowchart illustrating an exemplary method for encapsulating electrophoretic fluid.

[0014] Figure 4A This illustrates the size distribution of droplet intermediates in an exemplary method for manufacturing microcapsules according to this application. Figure 4B Display by Figure 4A The size distribution of microcapsules manufactured from tiny droplets.

[0015] Figure 5A shows the use Figure 4B A micrograph of the dried coating, fabricated in a capsule, dispersed in a polyurethane binder and incorporated into the test pixel. Figure 5B shows a scanning electron microscope (SEM) cross-section of the coating of Figure 5A.

[0016] Figure 6A An exemplary waveform is described for driving an electrophoretic display, including an encapsulated electrophoretic medium, to achieve a red display state. Figure 6BDescribes the waveform used to drive the electrophoretic medium of the package to achieve a white display state. Figure 6C Describes the waveform used to drive the electrophoretic medium of the package to achieve a black display state.

[0017] Figure 7 The size distribution of nonionic polymer microcapsules is shown after screening with various sieve sizes and comparison with prior art capsules.

[0018] Figure 8A shows a micrograph of a dried coating fabricated from 15 μm-sieved nonionic polymer microcapsules and incorporated into the test pixel. Figure 8B shows a scanning electron microscope (SEM) cross-section of the coating from Figure 8A.

[0019] Detailed Explanation

[0020] In a first aspect, the present invention relates to novel electro-optic media based on electrophoretic fluid encapsulated within microcapsules of a nonionic polymer. These nonionic polymer capsules contrast with conventional polymer capsules containing ionizable groups, such as those found in gelatin and arabic capsules. The capsules disclosed herein are generally formed from aggregates of nonionic polymers (multiple nonionic polymers) encapsulating an inner phase comprising a mixture of a nonpolar solvent and more than two types of charged pigment particles. Surprisingly, it has been found that, when addressed with the same waveform, the microcapsules provide approximately the same (or better) electro-optic performance compared to test holes or micropores incorporating the same fluid. In other words, the encapsulation process does not drastically alter the mechanism of pigment movement induced by the electrical addressing of the display. This "drop-in" capability means that the encapsulation media of the present invention can be used in existing infrastructures, such as backplanes and drivers.

[0021] Unbound by any particular theory, it appears unlikely that the nonionic microcapsule walls would interfere with the charge balance that must be maintained within the electrophoretic fluid, especially when complex outcomes are expected, such as in multicolor displays. Therefore, electro-optic media can be coated onto large surfaces and laminated with electrodes and / or other layers to create a variety of electro-optic devices, including daylight-readable displays and smart windows.

[0022] Electrophoretic displays typically comprise a layer of electrophoretic material 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 of these electrode layers are patterned to define display pixels. For example, one electrode layer may be patterned as elongated row electrodes, while the other is 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 commonly, 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. In another type of electrophoretic display, intended for use with a stylus, printhead, or similar movable electrodes separate from the display, only one of the layers adjacent to the electrophoretic layer includes electrodes, and the layers on opposite sides of the electrophoretic layer are generally protective layers designed to prevent damage to the electrophoretic layer by the movable electrodes.

[0023] Traditional microcapsule-based electrophoretic display (EPID) is shown in Figure 1A The display 100 typically includes a layer of electrophoretic material 130 and at least two other layers 110 and 120 disposed on opposite sides of the electrophoretic material 130, at least one of which is an electrode layer, for example... Figure 1A Layer 110 is depicted. The front electrode 110 may represent the viewing side of the display 100; in this case, the front electrode 110 may be a transparent conductor, such as indium tin oxide (ITO) (which in some cases may be deposited on a transparent substrate such as polyethylene terephthalate (PET)). Other flexible conductive materials, such as conductive polymers or polymers with conductive additives, may be used for the front electrode. Figure 1A As described, this EPD also includes a backplane 150 containing a plurality of driving electrodes 153 and a substrate layer 157. A layer of electrophoretic material 130 may include microcapsules 133 containing electrophoretic pigment white particles 135, black particles 137, and a solvent, and the microcapsules 133 are dispersed in a polymeric binder 139. Generally, the pigment particles 137 and 135 are controlled (displaced) by an electric field generated between the front electrode 110 and the pixel electrode 153. In many conventional EPDs, an electrically driven waveform is transmitted to the pixel electrode 153 via conductive traces (not shown) coupled to a thin-film transistor (TFT), which allows the pixel electrode to be addressed in a row-column addressing scheme. In some embodiments, the front electrode 110 is simply grounded and the image is driven by providing positive and negative potentials to the individually addressable pixel electrode 153. In other embodiments, a potential may also be applied to the front electrode 110 to provide a greater variation in the electric field that can be provided between the front electrode and the pixel electrode 153. In some embodiments, such as Figure 1B As shown, the third (red particle) 132 can be included in the electrophoresis display.

[0024] In many implementations, such Figure 2 As shown, the TFT array forms an active matrix for image driving. For example, each pixel electrode ( Figure 1A 153) is coupled to a thin-film transistor 210 patterned into an array and connected to an elongated row electrode 220 and an elongated column electrode 230 extending perpendicularly to the row electrode 220. In some embodiments, the pixel comprises a transistor made of metal oxide. In some embodiments, the pixel comprises a transistor formed of a doped polymer. In some embodiments, one electrode layer has the form of a single continuous electrode, and another electrode layer is patterned into a pixel electrode matrix, each pixel electrode defining a pixel of the display. Figure 2 As shown, the data (source) driver 250 is connected to the column electrode 230 and provides the source voltage to all TFTs in the column to be addressed. The scan (gate) driver 240 is connected to the row electrode 220 to provide a bias voltage that will turn on (or turn off) the gate of each TFT along that row. Of course, the positions of the data and source drivers are arbitrary; they can be derived from... Figure 2 The positions shown are interchanged. The gate scan rate is typically around 60-100 Hz, but in some cases, a faster or slower scan may be appropriate.

[0025] Generally, making the gate-source voltage positive allows the source voltage to short-circuit the drain. Making the gate negative relative to the source causes the drain-source current to decrease and the drain to float effectively. Because the scan driver operates sequentially, there is generally some measurable delay in the update time between the top and bottom row electrodes. It should be understood that the allocation of "row" and "column" electrodes is somewhat arbitrary and TFT arrays can be fabricated with the roles of row and column electrodes interchanged. In some embodiments, the TFT array is substantially flexible; however, individual components, such as individual pixel transistors or driving circuitry, may not be flexible. Flexible traces used to provide voltage to individual pixels can be formed from flexible materials, such as conductive polymers, or polymers doped with conductive materials such as metal particles, nanoparticles, nanowires, nanotubes, graphite, and graphene. In some embodiments, the TFT can be fabricated from organic thin-film transistors.

[0026] Although traditional EPID media are described as "black / white," they are generally driven to multiple different states between black and white to obtain various hues or "grayscales." Furthermore, a given pixel can be driven between a first grayscale state and a second grayscale state (which includes the white and black endpoints) by driving the pixel through a transition from an initial grayscale level to a final grayscale level (which may or may not be different from the initial grayscale level). The term "waveform" will be used to describe the curve of the entire voltage versus time used to achieve the transition from a particular initial grayscale level to a particular final grayscale level. Generally, such a waveform will contain multiple waveform units; where these units are substantially rectangular (i.e., where a given unit involves the application of a constant voltage over a period of time); said units may be referred to as "pulses" or "drive pulses."

[0027] The term "gray state" is used here in its conventional sense in the field of imaging to refer to the state intermediate between the two extreme optical states of a pixel, and does not necessarily imply a black-and-white transition between these two extreme states. For example, electro-optic displays are known to use variable transmission windows, where the extreme states are substantially transparent and substantially opaque, such that the intermediate "gray state" would be partially transmissive, but the color might not actually be gray. In fact, if the particles used are light-scattering, the partially transmissive "gray state" could actually be white. The term "monochrome" may be used below to refer to a driving scheme that drives pixels only to their two extreme optical states, without any intermediate gray state.

[0028] The terms “bistable” and “bistable” are used herein in their conventional sense in the art to refer to a display comprising display units having first and second display states that are different in at least one optical property, and such that after any given unit is driven to present its first or second display state by means of an addressing pulse of finite duration, the state will persist for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display unit after the addressing pulse terminates. U.S. Patent No. 7,170,670 discloses some particle-based electrophoretic displays capable of displaying grayscale that are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true for some other types of electro-optical displays. This type of display is appropriately referred to as “multistable” rather than bistable; however, for convenience, the term “bistable” may be used herein to cover both bistable and multistable displays.

[0029] Numerous patents and applications assigned to or in the name of the Massachusetts Institute of Technology (MIT) and E Ink Corporation describe various techniques for encapsulating electrophoretic and other electro-optic media. Such encapsulation media comprise a plurality of small capsules, each capsule containing an inner phase of particles that electrophoretically migrate in a fluid medium, and a capsule wall surrounding the inner phase. Some of the materials and techniques described in the following patents and applications are relevant to the manufacture of the variable transmission device described herein, including:

[0030] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, 5,961,804, 6,017,584, 6,120,588, 6,120,839, 6,262,706, 6,262,833, 6,300,932, 6,323,989, 6,377,387, 6,515,649, 6,538,801, 6 ,580,545、6,652,075、6,693,620、6,721,083、6,727,881、6,822,782、6,870,661、7,002,728、7,038,655、7,170,670、7,180,649、7,230,750、7,230,751、7,23 6,290, 7,247,379, 7,312,916, 7,375,875, 7,411,720, 7,532,388, 7,679,814, 7,746,544, 7,848,006, 7,903,319, 8,018,640, 8,115,729, 8,199,395, 8,270,0 U.S. Patents Nos. 64 and 8,305,341; and U.S. Patent Applications Nos. 2005 / 0012980, 2008 / 0266245, 2009 / 0009852, 2009 / 0206499, 2009 / 0225398, 2010 / 0148385, 2010 / 0207073, and 2011 / 0012825 are published;

[0031] (b) Encapsulation, adhesives, and encapsulation methods; see, for example, sections 5,930,026, 6,067,185, 6,130,774, 6,172,798, 6,249,271, 6,327,072, 6,392,785, 6,392,786, 6,459,418, 6,839,158, 6,866,760, 6,922,276, 6,958,848, 6,987,603, 7,061,663, 7,071,913, 7,079,305, 7,109,968, 7,110,164, 7,184,197, 7,202,991, 7 U.S. Patent Nos. 242,513, 7,304,634, 7,339,715, 7,391,555, 7,411,719, 7,477,444, 7,561,324, 7,848,007, 7,910,175, 7,952,790, 7,955,532, 8,035,886, 8,129,655, 8,446,664, and 9,005,494; and U.S. Patent Application Publications Nos. 2005 / 0156340, 2007 / 0091417, 2008 / 0130092, 2009 / 0122389, and 2011 / 0286081;

[0032] (c) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patents 6,982,178 and 7,839,564;

[0033] (d) Backplane, adhesive layer and other auxiliary layers and methods for display; see, for example, U.S. Patents 7,116,318 and 7,535,624;

[0034] (e) Color formation and color adjustment; see, for example, U.S. Patents 7,075,502 and 7,839,564;

[0035] (f) A method for driving a display; see, for example, U.S. Patents 7,012,600 and 7,453,445;

[0036] (g) Applications of the display; see, for example, U.S. Patents 7,312,784 and 8,009,348; and

[0037] (h) Non-electrophoretic displays, such as those described in U.S. Patent Nos. 6,241,921, 6,950,220, 7,420,549 and 8,319,759; and U.S. Patent Application Publication No. 2012 / 0293858.

[0038] Electrophoretic fluid

[0039] The internal phase of the electro-optic medium comprises charged pigment particles dispersed in a suspension solvent. In an exemplary embodiment, the solvent dispersing the three types of pigment particles is transparent and colorless, and can be a single liquid or a combination of two or more liquids. It preferably has a low viscosity and, for high particle mobility, a dielectric constant of about 2 to about 30, preferably about 2 to about 15. Examples of suitable dielectric solvents include hydrocarbons, such as… (Sigma-Aldrich), decahydronaphthalene (DECALIN), 5-ethylidene-2-norbornene, fatty oils, paraffin oils; silicone fluids; aromatic hydrocarbons, such as toluene, xylene, phenylxylene ethane, dodecylbenzene and alkylnaphthalene; halogenated solvents, such as perfluoronaphthene, perfluorotoluene, perfluoroxylene, dichlorobenzotrifluoride, 3,4,5-trichlorobenzotrifluoride, chloropentafluorobenzene, dichlorononane, pentachlorobenzene; and perfluorinated solvents, such as FC-43, FC-70 and FC-5060 from (3M Company, St. Paul, MN); low molecular weight halogenated polymers, such as poly(perfluoropropylene oxide) (TCI America, Portland, OR); poly(chlorotrifluoroethylene), such as Halocarbon Oils (Halocarbon Product Corp., River Edge, NJ); perfluoropolyalkyl ethers, such as Galden (Ausimont USA, Thorofare, NJ) or Krytox Oils and Greases K-fluid series (DuPont, Wilmington, DE); silicone oils based on polydimethylsiloxane, such as DC-200 (Dow Corning, Midland, MI).

[0040] The refractive index of the internal phase can be altered by adding a refractive index matching agent, such as one obtained from Cargille-Sacher Laboratories Inc. (Cedar Grove, New Jersey). Refractive index matched fluid.

[0041] Colored pigment particles

[0042] Charged pigment particles can have a variety of colors and compositions. Additionally, charged pigment particles can be surface-functionalized with polymers to improve their state stability. Such pigments are described in U.S. Patent No. 9,921,451, which is incorporated herein by reference in its entirety. As anticipated above, the electrophoretic fluid forming the inner phase of the microcapsules comprises three or more types of charged pigment particles dispersed in a suspension solvent. For ease of description, the three types of pigment particles may refer to white particles, black particles, and colored particles. This configuration in… Figure 1B For example, in addition to the conventional white particles 135 and black particles 137, red particles 132 are also present. However, it should be understood that the scope of the invention broadly includes pigment particles of any color, as long as the three types of pigment particles have visually contrasting colors. For example, the electrophoretic fluid may include a group of particles consisting of reflective white particles and absorbent particles of cyan, yellow, and magenta. Alternatively, the electrophoretic fluid may include a group of particles consisting of absorbent black particles and reflective particles of red, yellow, and blue.

[0043] For example, if the charged particles are white, they can be formed from inorganic pigments such as TiO2, ZrO2, ZnO, Al2O3, Sb2O3, BaSO4, PbSO4, etc. They can also be polymer particles with high refractive indices (>1.5) and specific sizes (>100 nm) to exhibit whiteness, or composite particles designed to have the desired refractive index. Regarding black charged particles, they can be formed from CI pigments 26 or 28 (e.g., manganese ferrite black spinel or copper chromite black spinel) or carbon black. A third type of pigment particle can have colors such as red, green, blue, magenta, cyan, or yellow. Pigments used for this type of particle may include, but are not limited to, CI pigments PR 254, PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY138, PY150, PY155, or PY20. Commonly used organic pigments are 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 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, Hostaperm Green GNX, BASF Irgazine Red L 3630, Cinquasia Red L 4100HD and Irgazin Red L 3660HD; Sun Chemical Phthalocyanine Blue, Phthalocyanine Green, Diarylide Yellow or Diarylide AAOT Yellow.

[0044] The percentages of the three types of pigment particles in the electrophoretic fluid can vary. For example, black particles may comprise about 0.1% to 10% of the electrophoretic fluid volume, preferably 0.5% to 5%; white particles may comprise about 1% to 50% of the fluid volume, preferably 5% to 15%; and colored particles may comprise 2% to 20% of the fluid volume, preferably 4% to 10%. Other particulate matter may be present in the fluid as additives to enhance the performance of the display device, such as switching speed, imaging bistableness, and reliability.

[0045] In a representative embodiment, two of the three types of pigment particles carry opposite charge polarities, and a third type of pigment particle is slightly charged. The term "slightly charged" is defined as the third type carrying a fraction of the charge of the more heavily charged particles of the first two types. For example, if black particles are positively charged and white particles are negatively charged, then the colored pigment particles are slightly charged. In other words, the black and white particles carry a much stronger charge than the colored particles. In an exemplary embodiment, the colored pigment particles carry a charge that is less than 75%, less than 50%, less than 40%, or less than 30% of the charge of the more heavily charged ions in the white and black particles. Generally, the charge of a "slightly charged" particle is half to one-third of that of a more heavily charged particle. Furthermore, the charge polarity of the third type of slightly charged particles is the same as that of either of the other two types of more heavily charged particles.

[0046] Based on the desired charge polarity and charge level of the particles, the surface of charged particles can be modified using known techniques, such as those described in U.S. Patents 6,822,782, 7,002,728, 9,366,935, and 9,372,380, and U.S. Publication 2014-0011913. The particles may exhibit a natural charge, or may be explicitly charged using a charge control agent, or may acquire a charge when suspended in a solvent. Suitable charge control agents are well known in the art; they may be polymeric or nonpolymeric in nature, or ionic or nonionic. Examples of charge control agents include, but are not limited to, Solsperse 17000 (active polymer dispersant), Solsperse 9000 (active polymer dispersant), OLOA 11000 (succinimide ashless dispersant), Unithox 750 (ethoxide), Span 85 (sorbitan trioleate), Petronate L (sodium sulfonate), Alcolec LV30 (soy lecithin), Petrostep B100 (petroleum sulfonate) or B70 (barium sulfonate), Aerosol OT, polyisobutylene derivatives, or poly(ethylene copoly-butene) derivatives. In addition to the suspending solvent and charged pigment particles, the internal phase may include stabilizers, surfactants, and charge control agents. Stabilizing materials, when dispersed in a solvent, can be adsorbed onto the charged pigment particles. This stabilizing material keeps the particles separated from each other, such that the variable transmission medium is substantially non-transmissive when the particles are in their dispersed state.

[0047] As is known in the art, the dispersion of charged particles (typically carbon black, as described above) in a low dielectric constant solvent can be aided by surfactants. Such surfactants typically comprise a polar “head group” and a nonpolar “tail group” compatible with or soluble in the solvent. In this invention, it is preferred that the nonpolar tail group is a saturated or unsaturated hydrocarbon moiety, or another group soluble in hydrocarbon solvents such as poly(dialkylsiloxane). The polar group can be any polar organic functional group, including ionic materials such as ammonium, sulfonate, or phosphonate, or acidic or basic groups. Particularly preferred head groups are carboxylic acid groups or carboxylate groups. Stabilizers suitable for this invention include polyisobutylene and polystyrene. In some embodiments, dispersants such as polyisobutylene succinimide and / or sorbitan trioleate and / or 2-hexyldecanoic acid are added.

[0048] The three types of pigment particles can have different sizes. In one embodiment, one of the three types of pigment particles is larger than the other two. It should be noted that, of the three types of pigment particles, the slightly charged type of particles preferably has a larger size. For example, both black and white particles are relatively small, and their size (by dynamic light scattering testing) can be from about 50 nm to about 800 nm, and more preferably from about 200 nm to about 700 nm. In this exemplary embodiment, the slightly charged colored particles are preferably about 2 to about 50 times larger than the black and white particles, more preferably about 2 to about 10 times larger.

[0049] In the context of this invention, the term "threshold voltage" is defined as the maximum bias voltage that can be applied to a group of pigment particles without causing the pigment particles to appear on the viewing side of the display device. The term "viewing side" refers to the side of the display device from which the viewer sees the image. In one aspect of this application, at least one of three types of pigment particles can exhibit a threshold voltage under a triangular voltage drive test. The threshold voltage is an inherent characteristic of charged pigment particles or an additive-induced property. In the former case, the generation of the threshold depends on some kind of attraction between particles or between particles and certain substrate surfaces. The threshold can also be generated via the interaction of two types of particles with opposite charges. In the latter case mentioned above, to obtain the threshold voltage, a thresholding agent that induces or enhances the threshold characteristics of the electrophoretic fluid can be added. The thresholding agent can be any material soluble in or dispersed in the electrophoretic fluid and carrying or inducing a charge opposite to the charge of the charged pigment particles. The thresholding agent can be sensitive or insensitive to changes in the applied voltage. The term "thresholding agent" can broadly include dyes or pigments, electrolytes or polyelectrolytes, polymers, oligomers, surfactants, charge control agents, etc. Further information regarding threshold agents can be found in U.S. Patent No. 8,115,729.

[0050] Capsule material

[0051] In one aspect of the invention, the nonionic capsule wall is made of one or more starting homopolymers or copolymers that are water-soluble or water-dispersible in a pH-neutral aqueous solution and are nonionic. In one embodiment, the starting polymer is substantially uncharged in an aqueous solution with a pH of about 2 to 12. In other non-exclusive embodiments, the starting polymer is substantially uncharged in an aqueous solution with a pH of about 3 to 11, 4 to 10, 5 to 9, or 6 to 8. Optionally or alternatively, the starting polymer is substantially uncharged under the operating conditions of the electrophoretic medium into which the capsule will be incorporated. In a preferred embodiment, at least one of the nonionic wall polymers is characterized by three or more functional groups capable of forming covalent bonds with a crosslinking agent to strengthen the capsule wall. Generally, functional groups include alcohol hydroxyl (-OH) moieties bonded to saturated carbon, which are either part of the polymer chain or linked thereto via bridging moieties.

[0052] It should be understood that starting polymers may include a small number of charged functional groups in some cases, provided that the amount of charge does not significantly degrade the capsule's performance. For example, the starting polymer may be a polyol containing a carboxyl or amino moiety, which is ionized at the pH of the electrophoretic medium, but the number of ionizable functional groups is too small to negatively affect the properties of the non-ionized capsule in the way seen, for example, with gelatin / arabi capsules. In some cases, the starting polymer may include functional groups that, while charged within a specific pH range, create a neutral moiety once incorporated into the capsule wall, emphasizing the neutrality of this characteristic in the final product. Generally, this type of functional group includes carboxylic esters incorporated into the ester moiety and amino groups that become part of an amide or carbamate moiety within the capsule wall of the final product.

[0053] In this specification, unless otherwise stated, the term "polymer" includes molecules consisting of at least 50 repeating subunits, such as polyvinyl lactams such as polyvinylpyrrolidone (PVP); hydrophilic polyethers such as polyethylene glycol (PEG), polyethylene oxide-polypropylene oxide (PEO-PPO), polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO), vinylpyrrolidone-vinyl acetate copolymers, polysaccharides, and water-soluble polysiloxanes.

[0054] Polyhydroxy polymers, also known as polyols, generally include those with 1,2- and / or 1,3-diol structures, such as those with the formula (CH2CHOH). nPolyvinyl alcohol (PVOH) is a compound containing n alcohol groups, where n can be hundreds or even thousands depending on the molecular weight of the PVOH. In the case of preparing PVOH by hydrolyzing the corresponding homopolymer polyvinyl acetate, the PVOH may contain less than 50% polyvinyl acetate units, particularly less than 20%. In some embodiments, the polyvinyl alcohol may also contain low proportions, for example up to 20%, or optionally up to 10% or up to 5% copolymer units of ethylene, propylene, acrylamide, methacrylamide, dimethacrylamide, hydroxyethyl methacrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, vinylpyrrolidone, hydroxyethyl acrylate, allyl alcohol, styrene, or similar commonly used comonomers. Copolymers of hydrolyzed or partially hydrolyzed vinyl acetate may also be used, which can be obtained, for example, as hydrolyzed ethylene-vinyl acetate (EVA), or vinyl chloride-vinyl acetate, N-vinylpyrrolidone-vinyl acetate, and maleic anhydride-vinyl acetate. Polysaccharides provide another class of preferred polyols, such as ethyl cellulose, hydroxypropyl methyl cellulose, guar gum, dextrin, starch, and other related materials such as those well known in the art.

[0055] Preferably, the starting polymers (multiple starting polymers) have an average molecular weight of at least about 10,000 Daltons. The upper limit of their average molecular weight may be up to 25,000 Daltons, 50,000 Daltons, or 75,000 Daltons, although an upper limit of 100,000 Daltons or higher has also been considered.

[0056] Crosslinking agents capable of reacting with the hydroxyl groups of polyol-based polymers and forming covalent bonds include molecules with two or more reactive carbonyl groups, such as saturated dialdehydes with 2 to 6 carbon atoms. The reaction between the alcohol group of the polyol and the carbonyl moiety of the dialdehyde forms a crosslink that enhances the microcapsule structure. Other possible crosslinking agents include organotitanates or zirconates with boric acid. Stabilizing the polymer by heating and cooling steps is also possible, which can induce physical crosslinking, for example, by means of entanglement or hydrogen bonding. Configurations of starting polymers characterized by reactive groups other than hydroxyl groups are also considered, provided that the crosslinking agent includes a portion capable of reacting with such groups to form covalent bonds.

[0057] Encapsulated electrophoretic fluid

[0058] On the other hand, a method for encapsulating electrophoretic fluids is provided, which uses a coagulation method, also known as phase separation, to deposit one or more nonionic, water-soluble, or water-dispersible starting polymers onto emulsion droplets of the electrophoretic fluid. Coagulation involves separating the liquid phase of the coating material from the polymerization solution and encapsulating this phase as a coagulated layer around the suspended core droplets. For example, coagulation can occur by changing some system parameters such as temperature, pH, or composition, thereby adjusting the surface energy of the core droplets relative to the coating material. The coagulated layer is then solidified using thermal, crosslinking, and / or solvent removal techniques to produce product microcapsules, wherein the solidified coagulated layer has been transformed into a solidified capsule wall.

[0059] Figure 3 A representative embodiment of the method is described. An aqueous solution (30) of one or more water-dispersible starting polymers is prepared, then mixed with an electrophoretic fluid (32), and the resulting mixture is heated to a temperature above the lowest critical solution temperature (LCST) (34). The polymer aggregates, producing emulsified droplets. This method can be controlled by adding an aggregation inducing agent, such as a salt, to the polymer solution. The effectiveness of various salts in controlling LCST is described in the experimental Hofmeister series, as is well known in the art. A crosslinking agent (36) is then added, and the resulting mixture is reacted until the aggregated phase solidifies to form a capsule wall.

[0060] In one embodiment, curing occurs without heating, and the curing mixture reacts at its formation temperature or a lower temperature. In another embodiment, the curing mixture is heated directly or incrementally to a higher temperature (38), and then curing is allowed to proceed at that higher temperature until completion, at which point heating is stopped and the mixture is cooled spontaneously or by active thermal removal (39).

[0061] It has been found that better results are obtained when curing is carried out in the presence of heat. Without being bound by any particular theory, one possible explanation is that if heating is absent, the aggregated polymer on the outer layer of the capsule pre-coat tends to redissolve in the aqueous medium at a higher rate than the crosslinking reaction (multiple crosslinking reactions). The manufactured capsules are then separated by size screening or other size exclusion classification methods. Capsules larger than approximately 120 μm tend to be difficult to work with because they tend to rupture during shear stress treatment. Additionally, capsules larger than 100 μm are visible to the naked eye, and their presence may be perceived as ripples in the variable transmission membrane.

[0062] After sizing, the capsules are mixed with a binder to create a slurry for coating, such as using slot coating, blade coating, spin coating, etc. Alternatively, as described in U.S. Patent No. 9,835,925, which is incorporated herein by reference in its entirety. In some embodiments of this application, the binder comprises a polymer, such as a water-soluble polymer like cationically modified polyvinyl alcohol, or a latex, such as comprising a polyurethane material. As anticipated above, the capsules of this application perform unexpectedly well when evaluated with waveforms having the same structure as those used to drive the same electrophoretic fluid in test wells or micropores.

[0063] The following are representative embodiments illustrating aspects of the present invention. Example

[0064] Example 1 - Preparation of polyvinyl alcohol microcapsules

[0065] A solution of polyvinylpyrrolidone (112.0 g of a 20% solution, with an average molecular weight of 1.3 MDa) and polyvinyl alcohol (74.7 g of a 10% solution, Mowiol 23-88, obtained from Kuraray, Japan) was mixed and stirred at 4°C for 1 hour. Then, a sodium sulfate solution (88.36 g of a 16.7% aqueous solution) was added to produce a cloud point temperature of 25°C. The solution was stirred at 4°C until the precipitate dissolved. At this point, a three-pigment electrophoretic fluid (120 g, similar to the fluid described in U.S. Patent No. 8,717,664, which is incorporated herein by reference in its entirety) containing white, black, and red particles was added below the surface. The temperature was then increased to 9°C and the solution was stirred at 400 rpm for 9 minutes to form droplets.

[0066] Then, 30 g of a mixture containing 15.15 g of a 50% wt% glutaraldehyde aqueous solution, 1.52 g of 10% acetic acid, 0.27 g of 0.9% hydrogen chloride, and 13.36 g of water was added at 9°C. The resulting mixture was maintained at 9°C for 50 minutes, followed by raising the temperature to 15°C. After maintaining this temperature for 1 hour, the mixture was heated to 60°C and maintained at this temperature for 135 minutes, then cooled to 25°C. After 30 minutes, the capsules were collected by centrifugation and stored in a 5°C refrigerator for one week, followed by purification. The force required to rupture a single capsule, normalized relative to the capsule diameter, was approximately 48 N / m. Figure 4A and 4B This displays the size distribution of droplets and capsules in the material manufactured according to the above procedure. Figure 4A This shows the droplets before the capsule wall was formed using the present invention and gelatin as a control. Figure 4B This invention shows the end of the capsule wall formation reaction and after size classification by screening.

[0067] Microcapsule coating

[0068] After the microcapsules were prepared and separated, they were incorporated into a coating slurry containing 60 mg of cationic-modified polyvinyl alcohol polymer CM-318 (Kuraray, Japan) in aqueous solution. This slurry was then coated onto a 4 mm thick polyethylene terephthalate (PET) substrate with a transparent conductive indium tin oxide (ITO) coating to produce a specific gravity of 21 g / m³. 2 The resulting microcapsule coating was then combined with a carbon backing plate to form pixels.

[0069] Figure 5A shows a micrograph of the microcapsule coating, while Figure 5B shows a cross-section of the coating. As seen in Figure 5A, although there are many pores in the microcapsule coating, it is noteworthy that the coating is essentially a single layer. The cross-section shows that the dried microcapsules 500 have a flat appearance and form a uniform layer with a thickness of approximately 15 micrometers. For ease of observation, two capsules within the capsule layer are demarcated by white polygons.

[0070] Use such as Figures 6A-6C The conventional waveform switching described above forms the test pixels. The same electrophoretic fluid containing black, white, and red particles is also incorporated into micropores and gelatin / arabic capsules, and the resulting product forms pixels, which are then switched using the same conventional waveform used for the aforementioned microcapsules.

[0071] The performance of the test pixels is quantified according to the CIELAB (also known as CIE L*a*b*) color space and reported in Table 1 below:

[0072] Table 1. Comparison of CIELAB electro-optic properties of three-color electrophoretic media under different packaging structures.

[0073]

[0074] It can be seen that the micropores and polyvinyl alcohol capsules yield good white, black, and red states, producing the same colors as when addressed using the conventional voltage sequence of U.S. Patent No. 8,717,664. However, in this case, the gelatin / arabinogalactan capsules fail to achieve a neutral black or red state with a*>31. Clearly, when the same electrophoretic fluid is contained within the gelatin / arabinogalactan microcapsules, they behave very differently and fail to produce the correct colors. This is unexpected, as gelatin / arabinogalactan microcapsules have been shown to provide excellent performance for black and white displays and are believed to perform equally well in more complex electrophoretic fluids.

[0075] Without being bound by any particular theory, it is known that the charge on the microcapsule walls in gelatin / gum arabic is a function of pH. In coating slurries, the pH is generally adjusted to be alkaline to ensure that the carboxylic acid ester groups in the capsule walls are ionized. When these groups are charged (because they are at a high pH), the tendency for the capsules to adhere together is reduced, while at low pH, intercapsule adhesion can cause the slurry viscosity to be too high for effective coating. However, when the electrophoretic fluid contains more than two pigments, it may not be desirable to increase the pH of the coating solution, as the materials added to achieve this may interfere with the final performance of the electrophoretic display. In some cases, satisfactory performance can be restored by adjusting the addressing waveform and the desired optical state in the gelatin / gum arabic microcapsules, but generally, extensive chemical adjustments to the electrophoretic fluid itself are necessary. Coating slurries that are less sensitive to pH are preferred.

[0076] Furthermore, bladders with charged walls can also adhere to a substrate on which the bladder with charged walls is coated, thus losing the ability to effectively reassemble to form a single-layer coating. Although the manufacturing process can be controlled to produce a uniform coating of bladders with charged walls, it is generally much easier to produce a single-layer coating using bladders without wall charge.

[0077] It is also worth noting that the time required to form polyvinyl alcohol microcapsules is much shorter than that of conventional methods used to form gelatin / arabic capsules. Encapsulating a 120g batch of electrophoretic fluid into polyvinyl alcohol-based capsules takes approximately 4 hours, while the standard gelatin / arabic method typically takes more than 13 hours.

[0078] Example 2 - Difference in Reinforcing Capsule Size

[0079] Additional microcapsules with full-color (CMYW) electrophoretic fluid were formed using a nonionic polymer formulation similar to that of Example 1 above. The electrophoretic fluid was prepared by combining and mixing the following components overnight: a dispersion containing a white pigment (71.41 g of 55.71 wt% dispersion; polymer-coated TiO2 as described in US 8,582,196), a dispersion containing a magenta pigment (15.21 g of 24.99 wt% dispersion; CI Pigment Red 122 coated with vinyl benzyl chloride and lauryl methacrylate (LMA) as described in US Patent No. 9,697,778), and a dispersion containing a cyan pigment (14.23 g of 25.43 wt% dispersion; CI Pigment Red 122 coated with methyl methacrylate (MMA) and dimethylsiloxane). Pigment Blue 15:3), a dispersion containing yellow pigment (13.64 g of 35.62 wt% dispersion; CI Pigment Yellow 155 coated with polydimethylsiloxane capped with methyl methacrylate (MMA), 2,2,2-trifluoroethyl methacrylate (TFEM) and monomethacryloxypropyl), CCA111 (3.04 g of 75 wt% solution), and poly(isobutylene) with an average molecular weight greater than 500,000 (3.67 g of 9.94 wt% solution). (PIB solution in E) and with another E balance.

[0080] A solution of polyvinylpyrrolidone (74.07 g in a 15% solution, molecular weight 1.3 MDa) and polyvinyl alcohol (55.55 g in a 10% solution, Mowiol 23-88, obtained from Kuraray, Otemachi, Chiyoda, Tokyo, Japan) was mixed with 152.38 g of water and stirred at 5°C for 1 hour. Then, a sodium sulfate solution (88.36 g in a 16.7% aqueous solution) was added. The cloud point of the resulting mixture was ≤10°C. The solution was stirred at 5°C until the precipitate dissolved. At this point, 120 g of the above-mentioned electrophoretic fluid was added below the surface, and the solution was stirred at 600 rpm for 66 minutes to form droplets.

[0081] At this point, 30 g of a mixture comprising the following components was added at 5°C: 15.15 g of a 50% glutaraldehyde aqueous solution, 1.52 g of a 10% acetic acid solution, 0.27 g of a 0.9% hydrogen chloride solution, and 13.36 g of water. The pH was adjusted to 2.6 with 0.239 g of hydrogen chloride (37%). Next, the temperature was increased to 52°C and maintained at that temperature for 75 minutes, then cooled to 25°C. The formed cysts were collected and cleaned by sieving. The force required to rupture a single cyst, normalized relative to the cyst diameter, was approximately 335.1 N / m.

[0082] The fabricated capsules were washed and sieved to separate by size. In many cases, the fractions passing through the sieve included bursting capsules and polymer crosslinking blobs, which were practically unable to encapsulate the electrophoretic inner phase (charged pigment particles distributed in a hydrocarbon solvent). Different capsule fractions were collected using different sieves with various opening sizes (25 μm, 20 μm, 15 μm), and the capsule size distribution was measured (see [link to sieve]). Figure 7 For comparison, standard gelatin-gum arabic microcapsule formulations were also prepared using the above-described CMYW electrophoretic fluid and screened at 20 μm. Figure 7 The average SVD size distributions shown are 35 μm for the gelatin control, 31 μm for PVOH capsules screened at 25 μm, 26 μm for PVOH capsules screened at 20 μm, and 24 μm for PVOH capsules screened at 15 μm. Furthermore, the total encapsulation and separation time is significantly reduced compared to the standard gelatin-gum arabic procedure. For example, 120 g of electrophoretic fluid can be encapsulated in polyvinyl alcohol in approximately 3.5 hours, while the gelatin / gum arabic method typically requires more than 13 hours. Table 2 shows a comparison of the capsule size distributions of the PvOH capsules prepared as described above and screened at 15 μm with those of the standard gelatin-gum arabic microcapsules screened at 20 μm.

[0083] Table 2. Comparison of capsule size distribution between PvOH capsules screened at 15 μm and standard gelatin-gum arabic microcapsules screened at 20 μm. Both types of capsules were filled with an electrophoretic fluid comprising four different types of charged pigment particles.

[0084]

[0085] Further analysis of the quality balance of various methods showed that the PVOH encapsulation method improved the yield of the encapsulated electrophoretic medium compared to the standard gelatin encapsulation method. This resulted in less pigment waste, as it was not encapsulated during the process.

[0086] After the microcapsules were prepared and separated, they were incorporated into a coating slurry containing 60 mg of a modified polyvinyl alcohol polymer CM318 in aqueous solution. This slurry was then coated onto a 4 mil thick polyethylene terephthalate (PET) substrate with a transparent conductive indium tin oxide (ITO) coating to produce a 21 g / m³ coating. 2The coating weight. Using the method detailed in U.S. Patent No. 6,982,178, which is incorporated herein by reference in its entirety, the resulting microcapsule coating was constructed with a carbon backing plate to form a test pixel. The quality of the coating obtained by sieving PvOH capsules at 15 μm can be seen in Figures 8A and 8B. Furthermore, comparing Figures 8A and 8B with Figures 5A and 5B, it is clear that the sieving method results in a smaller and more uniform capsule distribution, producing very thin (12 μm) and regular monolayer capsules (see Figure 8B). In the cross-sectional view, exemplary white ellipses are drawn on the capsule layer to illustrate the approximate capsule size in the capsule layer (Figure 8B). Importantly, because the resulting capsules are smaller than standard pigment capsules, charged pigment particles can move back and forth across the viewing surface more quickly when driven by the standard voltage driving method, thereby improving the viewer's update experience.

[0087] Test pixels similar to those shown in Figures 8A and 8B are driven using a conventional waveform for four-particle full-color electrophoresis media, as described, for example, as in US 9,921,451, which is incorporated herein by reference in its entirety. When compared to a gelatin-gum arabic control, the PvOH capsules exhibit a slightly larger color gamut.

[0088] Table 3. Comparison of calculated color gamut and measured dSNAP values ​​of four-particle full-color electrophoretic media in PvOH and gelatin-gum arabic microcapsules.

[0089] Capsule wall material Color gamut Average dSNAP PvOH, 25μm sieve ～103964 5.0 PvOH, 20μm sieve ～72725 7.00 PvOH, 15μm sieve ～68132 7.25 Gelatin-gum arabic, 20μm sieve ～84000 5.5

[0090] Additionally, the switching speed of various test pixels was evaluated. When driven by an alternating primary color test pattern, at 18 and 42 frames, corresponding to switching times of ~500 and 210 ms respectively, the PvOH capsules showed a slightly higher color gamut than their gelatin-gum arabic counterparts. At the same frame rate, a higher color gamut indicates a faster switching speed for the PvOH capsules compared to the gelatin-gum arabic. At 18 frames, smaller PVOH fractions showed a higher color gamut, implying that smaller capsule sizes may potentially have a faster switching speed than the control.

[0091] Table 4. Color gamut calculations based on color saturation measurements of different frames in the color test pattern show that the switching speed of the same pigment is faster in PvOH capsules than in gelatin arabic capsules.

[0092]

[0093] It will be apparent to those skilled in the art that many changes and modifications can be made to the specific embodiments of the present invention described above without departing from the scope of the invention. Therefore, the entire foregoing description is to be interpreted as illustrative rather than restrictive.

Claims

1. An electrophoretic medium comprising a capsule and an adhesive surrounding the capsule, wherein, The capsule includes a capsule wall and an electrophoretic fluid encapsulated by the capsule wall, wherein: The capsule wall comprises a water-soluble or water-dispersible, cross-linked nonionic polymer; and The electrophoretic fluid comprises a suspension solvent, a first pigment particle, a second pigment particle, and a third pigment particle, wherein the first, second, and third particles are of different colors, are charged, are suspended in the electrophoretic fluid, and are able to move through the electrophoretic fluid when an electric field is applied to the capsule.

2. The electrophoretic medium according to claim 1, wherein the nonionic polymer is a polyol.

3. The electrophoretic medium according to claim 2, wherein the polyol is polyvinyl alcohol.

4. The electrophoretic medium according to claim 1, wherein the capsule wall comprises a solidified coagulated layer formed of a nonionic polymer and polyvinyl lactam.

5. The electrophoretic medium according to claim 4, wherein the polyvinyl lactam is polyvinylpyrrolidone.

6. The electrophoretic medium according to claim 1, wherein the capsule wall is cross-linked by reaction with dialdehyde.

7. The electrophoretic medium according to claim 6, wherein the dialdehyde is glutaraldehyde.

8. The electrophoretic medium according to claim 1, wherein the suspension solvent comprises hydrocarbons.

9. The electrophoretic medium according to claim 1, wherein the electrophoretic fluid further comprises fourth pigment particles.

10. An electrophoretic display comprising an electrophoretic dielectric layer according to claim 1, and at least one electrode disposed adjacent to the electrophoretic dielectric and arranged to apply an electric field to the electrophoretic dielectric.

11. The electrophoretic medium of claim 1, comprising capsules with an average diameter of 15 μm to 50 μm, wherein less than one-third of the capsules are less than 15 μm or greater than 50 μm by number.

12. An electrophoretic display comprising an electrophoretic dielectric layer according to claim 11, and at least one electrode disposed adjacent to the electrophoretic dielectric and arranged to apply an electric field to the electrophoretic dielectric.

13. A method for manufacturing the electrophoretic medium according to claim 1, the method comprising: Provide polymer solutions containing nonionic, water-soluble, or water-dispersible starting polymers in an aqueous solvent; Provides an electrophoretic fluid containing suspended solvents and pigment particles; Mixing polymer solutions and electrophoretic fluids to produce a reaction mixture; The reaction mixture is heated to a temperature above the minimum critical solution temperature of the polymer solution to form an oil-in-water emulsion containing the electrophoretic fluid; Adding a crosslinking agent to an oil-in-water emulsion to form a cured mixture; and The mixture is heated to cure it and form a capsule containing the electrophoretic medium.

14. The method of claim 13, wherein the polymer solution comprises polyvinyl alcohol.

15. The method of claim 13, wherein the polymer solution comprises a copolymer of vinyl acetate.

16. The method of claim 13, further comprising adding a second nonionic, water-soluble, or water-dispersible starting polymer to the polymer solution.

17. The method of claim 16, wherein the second nonionic, water-soluble, or water-dispersible starting polymer is polyvinylpyrrolidone.

18. The method according to claim 13, wherein the crosslinking agent is glutaraldehyde.

19. The method of claim 13, further comprising adding a coagulation inducer to the polymer solution.

20. The method of claim 19, wherein the coagulation inducer is a water-soluble or water-dispersible salt.

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