Electrophoretic medium comprising a cationic charge control agent

Abstract

An electrophoretic medium containing a plurality of charged pigment particles, a charge control agent, and a non-polar liquid is disclosed. The charge control agent (CCA) has a molecular structure comprising a quaternary ammonium functional group or an imidazolium cation, a hydrophobic tail group, and a counterion, the counterion being an anion, the anion being a conjugate base of an acid, the acid having a pKa less than or equal to -2.5. The charge control agent (CCA) has the following Formula IX, wherein R 11 is a hydrophobic moiety comprising a functional group selected from the group consisting of poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene), and wherein the counterion is trifluoromethanesulfonate.

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 604,274, filed November 30, 2023, which is incorporated in its entirety by reference, together with all other patents and patent applications disclosed herein. Invention Field

[0003] This invention relates to electrophoretic media for use in electro-optic devices, the electrophoretic media comprising a plurality of charged particles and a charge control agent in a nonpolar liquid. In one aspect, the invention relates to an electrophoretic media comprising a charge control agent and a counter ion, the charge control agent having a quaternary ammonium functional group or an imidazolium cation, the counter ion being an anion that is the conjugate base of an acid having a pKa less than or equal to -2.5. Background of the Invention

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

[0006] Particle-based electrophoretic displays have been a subject of in-depth research and development for many years. In such displays, multiple charged particles (sometimes called pigment particles or charged pigment particles) move through a fluid under the influence of an electric field. The electric field is typically provided by a conductive film or transistor, such as a field-effect transistor. Compared to liquid crystal displays (LCDs), electrophoretic displays offer good brightness and contrast, wide viewing angles, bistable states, and low power consumption. However, such electrophoretic displays have a slower switching speed than LCDs, and are generally too slow to display live video. Additionally, electrophoretic displays can become sluggish at low temperatures because the viscosity of the fluid restricts the movement of the electrophoretically charged particles. Despite these drawbacks, electrophoretic displays have been found to be used in everyday products such as e-books (electronic readers), mobile phones and phone cases, smart cards, signage, watches, shelf labels, and flash drives.

[0007] The term "grayscale" is used herein in its conventional sense within the imaging field to refer to an intermediate state between two extreme optical states of a pixel, and does not necessarily imply a black-and-white transition between these two extreme states. For example, several E Ink patents and published applications mentioned below describe electrophoretic displays where the extreme states are white and dark blue, making the intermediate "grayscale" actually a pale blue. In fact, as already mentioned, a change in optical state may not be a change in color at all. The terms "black" and "white" can be used below to refer to the two extreme optical states of a display and should be understood to generally include extreme optical states that are not strictly black and white, such as the aforementioned white and dark blue states. The term "monochrome" can be used below to refer to a driving scheme that drives pixels only to their two extreme optical states without an intermediate grayscale state.

[0008] In the sense that the material has a solid outer surface, some electro-optic materials are solid, although these materials may and often do have internal liquid- or gas-filled spaces. For convenience, such displays using solid electro-optic materials will be referred to as "solid-state electro-optic displays" below. Therefore, the term "solid-state electro-optic display" includes rotating dual-color element displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

[0009] The terms “bistable” and “bistable” are used herein in their conventional sense to refer to a display comprising display elements having a first display state and a second display state that are different in at least one optical property, such that after any given element is driven to present its first or second display state by an addressing pulse of finite duration, the state persists for at least several times, for example, at least four times, the shortest duration of the addressing pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of displaying grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and this is also true for some other types of electro-optical displays. This type of display is precisely referred to as “multistable” rather than bistable, but for convenience, the term “bistable” as used herein can be used to encompass both bistable and multistable displays.

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

[0011] Numerous patents and applications assigned to or attributed to MIT, E Ink, E Ink California, LLC., and related companies describe various techniques used in encapsulated electrophoretic media and microcell electrophoretic media, as well as other electro-optic media. Encapsulated electrophoretic media comprise numerous small capsules, each capsule containing an electrophoretic medium with particles capable of electrophoretic movement in a fluid medium, and a capsule wall surrounding the electrophoretic medium. Typically, the capsules themselves are held in a polymer binder to form a coherent layer between two electrodes. In microcell electrophoretic displays, charged particles and fluid are not encapsulated within microcapsules but are retained within a carrier medium, typically within multiple cavities formed within a polymer film [[Hereinafter, the term "microcavity electrophoretic display" may be used to encompass both encapsulated electrophoretic displays and microcell electrophoretic displays.]]. The techniques described in these patents and applications include:

[0012] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 7,002,728 and 7,679,814, and U.S. Patent Application Publications Nos. 2020 / 0355978, 2024 / 0279391, and 2023 / 0213790;

[0013] (b) Encapsulation, adhesives, and encapsulation methods; see, for example, U.S. Patents 6,922,276 and 7,411,719;

[0014] (c) Microunit structures, wall materials, and methods of forming microunits; see, for example, U.S. Patents 7,072,095 and 9,279,906;

[0015] (d) A method for filling and sealing microcells; see, for example, U.S. Patents 7,144,942 and 7,715,088;

[0016] (e) Films and subassemblies containing electro-optic materials; see, for example, U.S. Patents 6,982,178 and 7,839,564;

[0017] (f) Backplates, adhesive layers and other auxiliary layers and methods used in displays; see, for example, U.S. Patents 7,116,318 and 7,535,624;

[0018] (g) Color formation and color adjustment; see, for example, U.S. Patents 7,075,502 and 7,839,564.

[0019] (h) A method for driving a display; see, for example, U.S. Patents 7,012,600 and 7,453,445;

[0020] (i) Applications of displays; see, for example, U.S. Patents 7,312,784 and 8,009,348; and

[0021] (j) Non-electrophoretic displays, as described in U.S. Patent No. 6,241,921 and U.S. Patent Application Publication No. 2015 / 0277160; and applications of packaging and microcell technologies other than displays; see, for example, U.S. Patent Application Publication Nos. 2015 / 0005720 and 2016 / 0012710.

[0022] Although electrophoretic media are often opaque (e.g., because in many electrophoretic media, particles essentially block visible light from passing through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called "shutter mode," where one display state is substantially opaque and the other is transparent. See, for example, U.S. Patents 5,872,552; 6,130,774; 6,144,361; 6,172,798; 6,271,823; 6,225,971; and 6,184,856. Dielectric electrophoretic displays, similar to electrophoretic displays but dependent on changes in electric field strength, can operate in a similar mode; see U.S. Patent 4,418,346. Other types of electro-optic displays may also be able to operate in a shutter mode. Electro-optic media operating in shutter mode can be used in multilayer structures for full-color displays; in such structures, at least one layer adjacent to the viewing surface of the display operates in shutter mode to expose or hide a second layer further away from the viewing surface.

[0023] Encapsulated electrophoretic displays are generally not affected by the aggregation and sedimentation failure modes of conventional electrophoretic devices and offer further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates (the term "printing" is used to include all forms of printing and coating, including but not limited to: volumetric coating, such as patch die coating, slot or extrusion coating, cascade coating, curtain coating; roll coating, such as doctor blade roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal transfer printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques. Therefore, the resulting display can be flexible. Furthermore, because the display medium can be printed (using various methods), the display can be manufactured at low cost.

[0024] 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, and the other 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 may have the form of a single continuous electrode, and the other electrode layer may be patterned as a matrix of pixel electrodes, each of which defines a pixel of the display. In another type of electro-optical display, intended for use with a stylus, printhead, or similar removable electrodes separate from the display, only one layer adjacent to the electrophoretic layer includes electrodes, and the layers on opposite sides of the electrophoretic layer are typically protective layers designed to prevent damage to the electrophoretic layer by the removable electrodes.

[0025] The fabrication of a three-layer electrophoretic display typically involves at least one lamination operation. For example, several of the aforementioned MIT and E Ink patents and applications describe a method for manufacturing an encapsulated electrophoretic display in which an encapsulated electrophoretic medium, comprising a capsule contained in an adhesive, is coated onto a flexible substrate including an indium tin oxide (ITO) or similar conductive coating on a plastic film (which serves as the first electrode of the final display). The capsule / adhesive coating is then dried to form a coherent layer of electrophoretic medium firmly adhered to the substrate. Separately, a backplate is prepared comprising a pixel electrode array and conductors of a suitable arrangement connecting the pixel electrodes to driving circuitry. To form the final display, the substrate with the capsule / adhesive layer on it is laminated to the backplate using a laminating adhesive. (A very similar method can be used, replacing the backplate with a simple protective layer (such as a plastic film), to fabricate an electrophoretic display usable with a stylus or similar movable electrode that can slide across this protective layer.) In a preferred form of such a process, the backplane itself is flexible and is manufactured 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 laminating adhesives.

[0026] 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 utilize an active matrix backplane comprising an array of transistors or diodes and corresponding arrays of pixel electrodes, and “continuous” front electrodes (electrodes extending over multiple pixels and typically across the entire display) on a transparent substrate, components that are substantially identical to those in LCDs. 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 holes between them, placing the resulting assembly under vacuum, and immersing the assembly in a liquid crystal bath so that liquid crystal flows through the holes between the backplane and front electrodes. Finally, with the liquid crystal in place, the holes are sealed to provide the final display.

[0027] The LCD assembly process cannot be easily transferred to packaged displays. Because the electrophoretic medium is solid, it must exist between the backplate and the front electrode before the two integral components (backplate and front electrode) are fixed together. Furthermore, unlike liquid crystal materials, which simply need to be placed between the front electrode and the backplate without being connected to either, the packaged electrophoretic medium typically needs to be fixed to both; in most cases, the electrophoretic medium is formed on the front electrode, as this is generally easier than forming the medium on the backplate containing the circuitry. The front electrode / electrophoretic medium combination is then laminated to the backplate, usually by applying an adhesive to the entire surface of the electrophoretic medium and laminating it under heat, pressure, and possibly a vacuum. Therefore, most existing methods for the final lamination of solid-state electrophoretic displays are essentially batch processes, where the (typically) electro-optical medium, laminating adhesive, and backplate are immediately put together before final assembly, thus a method more suitable for mass production is desired.

[0028] Electro-optic displays, including electrophoretic displays, can be very expensive; for example, the cost of a color LCD in a portable computer typically accounts for a large portion of the overall computer cost. As the use of such displays expands to devices that are far less expensive than portable computers (such as mobile phones and personal digital assistants (PDAs)), there is immense pressure to reduce the cost of such displays. As mentioned above, the ability to form electrophoretic dielectric layers on flexible substrates using printing techniques, and the use of mass production techniques such as roll-to-roll coating using commercial equipment for producing coated paper, polymer films, and similar media, opens up possibilities for reducing the cost of electrophoretic components in displays.

[0029] Electro-optic displays typically comprise an electro-optic material layer and at least two other layers disposed opposite the electro-optic 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, and the other 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 may have the form of a single continuous electrode, and the other electrode layer may be patterned as a matrix of pixel electrodes, where each pixel electrode defines a pixel of the display. In another type of electro-optic display, intended for use with a stylus, printhead, or similar removable electrodes separate from the display, only one layer adjacent to the electro-optic layer includes electrodes, and the layer opposite the electro-optic layer is typically a protective layer designed to prevent damage to the electro-optic layer by the removable electrodes.

[0030] The aforementioned U.S. Patent No. 6,982,178 describes a method for assembling a solid-state electro-optic display (including an encapsulated electrophoretic display) that is well-suited for mass production. Essentially, the patent describes a so-called “front panel laminate” (“FPL”) comprising, in sequence: a light-transmitting conductive layer (first electrode 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, which is preferably flexible, meaning that the substrate can be manually wrapped around a roller with a diameter of (approximately) 10 inches (254 mm) without permanent deformation. In this patent and herein, the term “light-transmitting” means that the layer so specified transmits sufficient light that an observer can observe changes in the display state of the electro-optic dielectric through the layer, changes in which would typically be viewed through the conductive layer and an adjacent substrate (if present); where the electro-optic dielectric exhibits a change in reflectivity at non-visible wavelengths, the term “light-transmitting” should, of course, be interpreted as transmission at the corresponding non-visible wavelength. The substrate is typically a polymer film and is generally in the range of about 1 to about 25 mils (25 to 634 μm) thick, preferably about 2 to about 10 mils (51 to 254 μm). The conductive layer is preferably a thin metal or metal oxide layer, such as aluminum or ITO, or it may be a conductive polymer. Poly(ethylene terephthalate) (PET) films coated with aluminum or ITO are commercially available, for example, from El du Pont deNemours & Company of Wilmington, Delaware, under the name "aluminized Mylar" ("Mylar" is a registered trademark), and such commercial materials can be used in front panel laminates with good results.

[0031] Assembling an electro-optic display using such a front-panel laminate can be achieved by removing the release liner from the front-panel laminate and bringing the adhesive layer into contact with the backplate while effectively adhering the adhesive layer to the backplate, thereby 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-panel laminate can be mass-produced, typically using roll-to-roll coating technology, and then cut into sheets of any size required for use with a specific backplate.

[0032] U.S. Patent No. 7,561,324 describes a so-called "dual release sheet," which is essentially a simplified version of the front panel laminate of the aforementioned U.S. Patent No. 6,982,178. One form of the dual release sheet includes a solid electro-optic dielectric layer sandwiched between two adhesive layers, wherein one or both adhesive layers are covered by the release sheet. Another form of the dual release sheet includes a solid electro-optic dielectric layer sandwiched between two release sheets. Both forms of dual release sheets are intended for processes generally similar to those used for assembling electro-optic displays from the described front panel laminate, but involving two separate laminations; typically, in the first lamination, the dual release sheet is laminated to the front electrode to form a front sub-assembly, and then in the second lamination, the front sub-assembly is laminated to the back panel to form the final display, although the order of these two laminations can be reversed if desired.

[0033] U.S. Patent No. 7,839,564 describes a so-called "inverted front panel laminate," a variant of the front panel laminate described in U.S. Patent No. 6,982,178. This inverted front panel laminate sequentially comprises: at least one of a light-transmitting protective layer and a light-transmitting conductive layer; an adhesive layer; a solid electro-optic dielectric layer; and a release liner. This inverted front panel laminate is used to form an electro-optic display having a laminated adhesive layer between the electro-optic layer and the front electrode or front substrate; a second, typically thin, adhesive layer may or may not be present between the electro-optic layer and the backplate. Such an electro-optic display can combine good resolution with good low-temperature performance.

[0034] Full-color displays can be provided by using an electrophoretic medium containing multiple colored pigment particles with different electrophoretic mobilities. For example, U.S. Patent No. 9,921,451 teaches a color electrophoretic display comprising an electrophoretic medium including (a) one type of light-scattering pigment particles (typically white) and (b) three basic non-light-scattering pigment particles providing three subtractive primary colors. Color mixing is achieved using basic non-light-scattering particle types with subtractive primary colors, and more color results are provided on a single pixel than with a color filter. Electrophoretic media and electrophoretic devices exhibit complex behavior, especially those containing multiple sets of charged pigments with different charges and mobilities. Complex “waveforms” are required to drive the particles in different states. Coupled with the complexity of the electric field, the mixture of particles and fluid can exhibit unexpected behavior due to the interactions between charged pigment particles, charge control molecules, suspending liquid, and encapsulation materials when an electric field is applied. Generally, it is difficult to predict how an electrophoretic display will respond to changes in the composition of the electrophoretic medium. Typically, when an electrophoretic medium composition is modified by altering the chemical properties or content of a charge control agent, the charge of all types of pigment particles usually changes without exception. For example, in an electrophoretic medium containing multiple types of charged pigment particles, the zeta potential of all types of charged pigment particles is modified by changing the type of charge control agent. If it is desired to modify the zeta potential of only one type of charged pigment particle, it is usually necessary to modify the specific type of charged pigment particle itself, typically by preparing new pigment particles. Therefore, it would be beneficial to develop a method to control the zeta potential of a single type of charged pigment particle without significantly affecting the zeta potential of other types of charged pigment particles in the same electrophoretic medium. The inventors of this invention have surprisingly discovered that by using a polymeric charge control agent in an electrophoretic medium that modifies the zeta potential of one type of charged pigment particle without significantly modifying the zeta potential of other types of charged pigment particles, the electrophoretic medium contains the charge control agent, which has a quaternary ammonium head group or an imidazolium cationic head group, a hydrophobic tail group, and a counterion, wherein the counterion is an anion and the anion is a conjugate base of an acid with a pKa less than or equal to -2.5. Furthermore, the inventors of this invention have surprisingly discovered that, compared to electro-optic displays containing similar electrophoretic media with charge control agents having similar molecular structures but different counterions, the corresponding electro-optic display provides a wider color gamut by using an electrophoretic medium containing multiple charged pigment particles, a nonpolar liquid, and a polymeric charge control agent, wherein the polymeric charge control agent has a quaternary ammonium head group or an imidazolium cationic head group, a hydrophobic tail group, and a counterion as an anion, wherein the anion is a conjugate base of an acid with a pKa less than or equal to -2.5. Invention Overview

[0036] On one hand, the present invention provides an electrophoretic medium comprising a plurality of charged particles, a charge control agent, and a nonpolar liquid. When an electric field is applied, the plurality of charged particles are able to move through the nonpolar liquid. The charge control agent has a molecular structure comprising a quaternary ammonium functional group or an imidazolium cation, a hydrophobic tail group, and a counter ion. The counter ion of the charge control agent is an anion, which is a conjugate base of an acid, wherein the acid has a pKa less than or equal to -2.5, or between -2.5 and -16. The counter ion of the charge control agent may be selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonylimide, sulfate, perchlorate, chloride, bromide, and iodide ions.

[0037] The charge control agent may be a molecule selected from branched polyethyleneimine derivatives, molecules represented by formula I, molecules represented by formula II, molecules represented by formula III, molecules represented by formula IV, and molecules represented by formula V.

[0038]

[0039]

[0040]

[0041]

[0042]

[0043] The branched polyethyleneimine derivative has a molecular structure comprising one or more quaternary ammonium functional groups and one or more hydrophobic moieties. R1 is independently selected from aryl and alkyl groups, the alkyl group having 1 to 10 carbon atoms; m is an integer from 0 to 3; Z is one of branched or unbranched alkyldiyl groups; n is an integer from 3 to 20; Q is a moiety selected from esters, thioesters, amides, imides, ureas, and carbamates; R2 is the hydrophobic moieties; R3, R4, and R5 are selected from alkyl and aryl groups having 1 to 20 carbon atoms; each R6 and R7 is independently selected from alkyl, aryl, and -(Z) groups having 1 to 20 carbon atoms. n -Q-R2, and at least one of R6 and R7 is -(Z). n -Q-R2; and Y- is a counter ion.

[0044] The hydrophobic portion of the branched polyethyleneimine derivative and the hydrophobic portion R2 of formulas I to V can be selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. The hydrophobic portion R2 of formulas I to V may have 50 to 1000 carbon atoms or 10 to 300 dimethylsiloxane groups. The hydrophobic portion of the branched polyethyleneimine derivative and the hydrophobic portion R2 of formulas I to V may be derived from monomers selected from castor oil acid, isobutylene, hydroxystearic acid, and combinations thereof.

[0045] The weight-average molecular weight of charge control agents represented by formulas I to V can be from 800 g / mol to 12000 g / mol. The weight-average molecular weight of charge control agents represented by formulas I to V can be greater than or equal to 1000 g / mol.

[0046] When the charge control agent is a branched polyethyleneimine derivative, the branched polyethyleneimine derivative may have more than one hydrophobic moiety and more than one quaternary ammonium functional group. The branched polyethyleneimine derivative may be formed from branched polyethyleneimine having primary, secondary, and tertiary amine functional groups. The more than one hydrophobic moiety of the branched polyethyleneimine derivative may be formed by reacting the primary and / or secondary amine groups of the branched polyethyleneimine with monomers selected from castor oil acid, isobutylene, hydroxystearic acid, and combinations thereof. The more than one quaternary ammonium functional group of the branched polyethyleneimine derivative may be formed by alkylation of the tertiary amine functional group of the branched polyethyleneimine. The counter ion of the quaternary ammonium functional group of the branched polyethyleneimine derivative may be selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide ions. The number average molecular weight of the branched polyethyleneimine derivative may be higher than 1000 g / mol.

[0047] The charge control agent can be a molecule represented by formula VI or formula VII. Each R8, R9, R 10 The group is independently selected from alkyl groups having 1 to 10 carbon atoms; o is an integer from 3 to 10.

[0048]

[0049]

[0050] R 11 This is the hydrophobic portion. The hydrophobic portion can be selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. The counterion Y- can be selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide ions. The groups R8, R9, and R of formulas VI and VII...10 It can be a methyl group, and the hydrophobic portion R 11 It may contain functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene), and the counter ion Y- may be selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide.

[0051] The charge control agent can be a molecule represented by formula VIII or formula IX.

[0052]

[0053]

[0054] Group R 11 It can be a hydrophobic portion containing functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion Y- can be trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, or iodide.

[0055] Charge control agents can be molecules represented by formula X or formula XI.

[0056]

[0057]

[0058] Group R 12 and R 13 It can be a hydrophobic portion containing functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion Y- can be trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, or iodide.

[0059] Charge control agents can be molecules represented by formula XII. The group R 14 It can be an alkyl group, said alkyl group having 1 to 10 carbon atoms. Group R 15 It can be a hydrophobic portion containing functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion Y- can be trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, or iodide.

[0060]

[0061] Charge control agents can be molecules represented by formula XIII. Each R 16 R 17 R 18It can be independently selected from alkyl groups, said alkyl groups having 1 to 10 carbon atoms. Group R 19 It can be a hydrophobic portion containing functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion Y- can be trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, or iodide. The group R... 16 R 17 R 18 Each can be methyl, ethyl, or phenyl, and the counter ion Y- can be trifluoromethanesulfonate.

[0062]

[0063] The electrophoretic medium of the present invention may further comprise a second charge control agent. The second charge control agent may comprise a hydrophobic portion and a head group, wherein the head group is selected from groups comprising anionic, nonionic, and cationic functional groups. The second charge control agent may comprise an ammonium cation, an acyclic secondary amide group, and a hydrophobic portion.

[0064] On the other hand, the present invention provides an electro-optic display comprising a first electrode layer, an electro-optic material layer, and a second electrode layer. The electro-optic material layer is disposed between the first electrode layer and the second electrode layer. The electrode layer is light-transmitting. The second electrode layer includes a plurality of pixel electrodes. The electro-optic material layer includes a plurality of microcapsules or a plurality of microunits. The first electrode layer and the second electrode layer are configured to apply an electric field across the electro-optic material layer. Each microcapsule or microunit contains an electrophoretic medium. The electrophoretic medium contains a plurality of charged particles, a charge control agent, and a nonpolar liquid. When an electric field is applied, the plurality of charged particles are capable of moving through the nonpolar liquid. The charge control agent has a molecular structure comprising a quaternary ammonium functional group or an imidazolium cation, a hydrophobic tail group, and a counter ion. The counter ion of the charge control agent is an anion, which is a conjugate base of an acid having a pKa less than or equal to -2.5, or between -2.5 and -16. The counter ion of the charge control agent may be selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonylimide, sulfate, perchlorate, chloride, bromide, and iodide. The charge control agent may be a molecule selected from branched polyethyleneimine derivatives, molecules represented by Formula I, Formula II, Formula III, Formula IV, and Formula V. The branched polyethyleneimine derivative has a molecular structure comprising one or more quaternary ammonium functional groups and one or more hydrophobic moieties. R1 is independently selected from aryl and alkyl groups, the alkyl group having 1 to 10 carbon atoms; m is an integer from 0 to 3; Z is one of branched or unbranched alkyldiyl groups; n is an integer from 3 to 20; Q is a moiety selected from esters, thioesters, amides, imides, ureas, and carbamates; R2 is a hydrophobic moiety; R3, R4, and R5 are selected from alkyl and aryl groups having 1 to 20 carbon atoms; each R6 and R7 is independently selected from alkyl, aryl, and -(Z) groups having 1 to 20 carbon atoms. n -Q-R2, and at least one of R6 and R7 is -(Z). n- Q-R2; and Y- is a counter ion. The hydrophobic portion of the branched polyethyleneimine derivative and the hydrophobic portion R2 of formulas I to V can be selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. The hydrophobic portion R2 of formulas I to V may have 50 to 1000 carbon atoms or 10 to 300 dimethylsiloxane groups. The hydrophobic portion of the branched polyethyleneimine derivative and the hydrophobic portion R2 of formulas I to V can be derived from monomers selected from castor oil acid, isobutylene, hydroxystearic acid, and combinations thereof. The weight-average molecular weight of the charge control agent as a molecule represented by formulas I to V can be from 800 g / mol to 12000 g / mol. The weight-average molecular weight of the charge control agent as a molecule represented by formulas I to V can be greater than or equal to 1000 g / mol.

[0065] In the case of an electro-optic device comprising multiple micro-units, each of the multiple micro-units includes a bottom layer, a partition wall, an opening, and a sealing layer, the sealing layer spanning the opening of each micro-unit.

[0066] In the case of an electro-optic device comprising multiple microcapsules, the electro-optic material layer may include multiple microcapsules and an adhesive. Brief description of the attached diagram

[0068] Figure 1 This is a side view of a color electro-optic display including an electrophoretic medium encapsulated in microcapsules. The color electrophoretic display sequentially comprises a first electrode layer, an electro-optic material layer, a first adhesive layer, and a second electrode layer.

[0069] Figure 2 This is a side view of a color electro-optic display including an electrophoretic medium encapsulated in microcapsules. The color electrophoretic display sequentially comprises a first electrode layer, a second adhesive layer, an electro-optic material layer, and the second electrode layer.

[0070] Figure 3 This is a side view of a color electro-optic display including an electrophoretic medium encapsulated in microcapsules. The color electrophoretic display sequentially includes a first electrode layer, an electro-optic material layer including a sealing layer, a first adhesive layer, and a second electrode layer.

[0071] Figure 4 This is a diagram illustrating the methylation reaction of a cationic charge control agent containing a methyl sulfate counterion.

[0072] Figure 5 This is a diagram illustrating the methylation reaction of a cationic charge control agent containing a trifluoromethanesulfonate counterion.

[0073] Figure 6 This is a graph showing the maximum zeta potential of various charged particles in various electrophoretic compositions.

[0074] Figure 7 The color gamut of the electrophoretic compositions of the present invention and comparison is shown at 0°C.

[0075] Figure 8 The color gamut of the electrophoretic compositions of the present invention and comparison is shown at 25°C.

[0076] Figure 9 The color gamut of the electrophoretic compositions of the present invention and comparison is shown at 50°C. Invention Details

[0078] In the detailed description below, numerous specific details are illustrated with examples to provide a thorough understanding of the teachings. However, it will be apparent to those skilled in the art that these teachings can be implemented without these details.

[0079] This invention provides an electrophoretic medium comprising pigment particles and a charge control agent. Particles that absorb, scatter, or reflect light at a broadband or selected wavelength are referred to herein as pigment particles. The electrophoretic medium may be incorporated into a display or into a front-panel laminate or an inverted front-panel laminate, which are then bonded to a backplate to form a display.

[0080] As used herein, a "head group" of a molecule refers to a functional group on the hydrophilic portion of the molecule, which contains both hydrophilic and hydrophobic portions. A molecule may have one or more head groups. The hydrophobic portion of a molecule is also called a "tail group."

[0081] Unless otherwise stated, the terms “molecular weight” or “MW” used herein refer to weight-average molecular weight. Weight-average molecular weight is measured by gel permeation chromatography.

[0082] As used in this article, the pKa terminology for a material is the negative logarithm of the acid dissociation constant (Ka) of that material in an aqueous solution at 25°C. The smaller the pKa value, the stronger the acid. Measured or predicted pKa values ​​for acids can be found in the literature. A negative pKa indicates a very strong acid. It is well known in chemistry that the conjugate base of a strong acid is a weak base.

[0083] Particles containing metal oxides (such as titanium oxide, aluminum oxide, zirconium oxide, etc.) or silica typically have acidic surfaces because they contain functional groups with OH bonds. Such particles typically have pKa values ​​of 2 to 6 in aqueous media. Conversely, organic pigment particles without metal oxides or silica on their surfaces have lower acidity (or neutral or basicity) and pKa values ​​higher than 6. The pKa of particles in aqueous media can be determined by potentiometric titration of an aqueous dispersion of the particles using alkaline or acidic solution titrants. Relevant examples of pKa determination are described in U.S. Patent No. 10,078,285B2.

[0084] The electrophoretic medium according to various embodiments of the present invention comprises a plurality of charged particles, a charge control agent, and a nonpolar liquid. The charge control agent has a molecular structure comprising a quaternary ammonium functional group or an imidazolium cation, a hydrophobic tail, and a counterion. The counterion of the charge control agent is an anion that is the conjugate base of an acid, and the pKa of the acid is less than or equal to -2.5. The pKa of the acid can be -2.5 to -16, -2.5 to -10, or -2.5 to -5. The counterion of the quaternary ammonium functional group or the counterion of the imidazolium cation can be selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide ions.

[0085] The charge control agent can be a molecule represented by formula I, formula II, formula III, formula IV or formula V.

[0086] In Formula I, R1 is independently selected from alkyl groups having 1 to 10 carbon atoms and aryl groups; m is an integer from 0 to 3; R2 is a hydrophobic moiety. The hydrophobic moiety R2 can be selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof; Z is one of branched or unbranched alkyldiyl groups; n is an integer from 3 to 20; Q is a moiety selected from esters, thioesters, amides, imides, ureas, and carbamates; the esters, thioesters, amides, imides, ureas, and carbamates can be part of a moiety containing a ring structure or part of a moiety not containing a ring structure. The number of atoms in the ring structure can be 4 to 8, 5 to 7, or 5 to 6.

[0087] In Formula II, group R3 and in Formula III, R4 and R5 are selected from alkyl and aryl groups having 1 to 20 carbon atoms. In Formulas IV and V, each R6 and R7 is independently selected from alkyl, aryl, and -(Z) groups having 1 to 20 carbon atoms. n At least one of -Q-R2, R6, and R7 is -(Z). n -Q-R2, and Y- is the counter ion.

[0088] In Formula I, group R1 can be a methyl, ethyl, propyl, phenyl, or benzyl group. If more than one alkyl group is attached to an amine atom of a quaternary ammonium group of Formula I, the alkyl groups can be the same or different. For example, Formula I can include a trimethylammonium cationic group, a triethylammonium cationic group, a dimethylethylammonium cationic group, etc. Groups (Z) of Formula I (and Formulas II to V) n It can be -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2-, etc. (Z) n It can be an unbranched group -(CH2). q - where q can be 1 to 20. Optionally, group (Z) n The Q moiety can be a branched alkyl diyl group, such as -CH2(CH3)CH2CH2-. The Q moiety can be represented by various nonionic polar functional groups, such as ester groups [-OC(O)-], thioester groups [-SC(O)-], tertiary amide groups [-N(alkyl)-C(O)-], carbamate groups [-NH-C(O)-O-] or [-OC(O)-NH-], urea groups [-NH-C(O)-NH-], and combinations thereof. The ester group, thioester group, urea group, tertiary amide group, carbamate group, and urea group can be cyclic or non-cyclic. The Q moiety can be represented by the succinimide structure of formula XIV. In this case, nitrogen and (Z) nThe carbon atoms of the group are bonded, and one of the carbon atoms of the ring is bonded to an atom of the hydrophobic portion R2. In formulas I to V.

[0089]

[0090] As indicated by the charge control agents represented by formulas I and V, the charge control agents used in the various embodiments of the present invention are not limited to monoquaternary ammonium materials or materials containing only one imidazolium cation. The materials may include, for example, bisquaternary ammonium salts, triquaternary ammonium salts, etc.

[0091] The charge control agent of the electrophoretic medium of the present invention can be a branched polyethyleneimine derivative having one or more quaternary ammonium functional groups and one or more hydrophobic moieties. The branched polyethyleneimine derivative can be formed from branched polyethyleneimine having primary, secondary, and tertiary amino groups. The number-average molecular weight of the branched polyethyleneimine derivative can be higher than 1000 g / mol.

[0092] The hydrophobic portion of a branched polyethyleneimine derivative can be selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. The hydrophobic portion of a branched polyethyleneimine derivative can be formed by reacting the primary or secondary amino groups of the branched polyethyleneimine with monomers or oligomers. Monomers can be selected from castor oil acid, isobutylene, hydroxystearic acid, and combinations thereof.

[0093] The quaternary ammonium functional groups of branched polyethyleneimine derivatives can be formed by alkylation reactions between the tertiary amino groups of branched polyethyleneimine and alkylating agents.

[0094] The counterions of the quaternary ammonium functional groups of branched polyethyleneimine derivatives can be selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide and iodide.

[0095] The charge control agent of the electrophoretic medium of the present invention can be represented by formula VI or formula VII. Each group R8, R9, R... in formulas VI and VII... 10 Independently selected from alkyl groups, said alkyl groups having 1 to 10 carbon atoms. The variable o is 3 to 20, or an integer from 3 to 10. Group R 11 This is a hydrophobic portion, selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. Hydrophobic portion R 11It may contain functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion of the molecule represented by formulas VI and VII may be trifluoromethanesulfonate. The counter ion may also be bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide.

[0096] The charge control agent of the electrophoretic medium of the present invention can be represented by formulas VIII and IX. In these molecules, the nitrogen of the quaternary ammonium functional group is bonded to three methyl groups. Group R 11 This is a hydrophobic portion, selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. Hydrophobic portion R 11 It may contain functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion of the molecule represented by formulas VIII and XI may be trifluoromethanesulfonate. The counter ion may also be bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide.

[0097] The charge control agent of the electrophoretic medium of the present invention can be a molecule represented by formula X or XI. In formula X, the nitrogen of the quaternary ammonium functional group is part of a six-membered ring, and it is also bonded to a methyl group. In formula XI, there are two quaternary ammonium functional groups, in which the nitrogen is part of a six-membered group and is also bonded to a methyl group. Group R 11 and R 12 It can be selected independently. Group R 11 and R 12 This is a hydrophobic portion, selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. Hydrophobic portion R 11 and R 12 It may contain functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion of the molecule represented by formulas X and XI may be trifluoromethanesulfonate. The counter ion may also be bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide.

[0098] The charge control agent of the electrophoretic medium of the present invention can be a molecule represented by formula XII. In this case, the molecule contains a hydrophobic portion (R... 15 A substituted succinimide bonded to a quaternary ammonium functional group. The molecule contains a quaternary ammonium functional group. The nitrogen of the quaternary ammonium functional group is bonded to the R group. 14 Bonding, group R 14 It is an alkyl group having 1 to 20 carbon atoms or 1 to 10 carbon atoms. The hydrophobic portion R... 15The hydrophobic portion can be selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. 15 It may contain functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion of the molecule represented by formula XII may be trifluoromethanesulfonate. The counter ion may also be bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide.

[0099] The charge control agent of the electrophoretic medium of the present invention can be a molecule represented by formula XIII. In this case, the molecule contains a hydrophobic portion (R... 19 A substituted succinimide bonded to a quaternary ammonium functional group. The molecule contains a quaternary ammonium functional group. The nitrogen of the quaternary ammonium functional group is bonded to the R group. 16 R 17 and R 18 Bonding. Each group R in formula XII 16 R 17 and R 18 The group is independently selected from alkyl groups, alkyl groups having 1 to 20 carbon atoms, or alkyl groups having 1 to 10 carbon atoms. The group R in formula XII... 16 R 17 and R 18 It can be a methyl group or an ethyl group. The hydrophobic portion R 19 The hydrophobic portion can be selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof. 19 It may contain functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene). The counter ion of the molecule represented by formula XIII may be trifluoromethanesulfonate. The counter ion may also be bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide, and iodide.

[0100] A typical color electro-optic display may have an electro-optic material layer containing an electrophoretic medium encapsulated in microcapsules or microcells, as described in U.S. Patent No. 6,982,178. Figure 1A side view of an example of a portion of a color electro-optic display with microcapsules is shown. The color electro-optic display 100 includes a first electrode layer 101 containing light-transmitting electrodes, an electro-optic material layer 102, a first adhesive layer 104, and a second electrode layer 103, the second electrode layer including a plurality of pixel electrodes. The first adhesive layer 104 connects the electro-optic material layer 102 to the second electrode layer. The electro-optic material layer 102 includes a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and includes an electrophoretic medium 122 having charged pigment particles and a charge control agent in a non-polar liquid. The electrophoretic medium 122 includes a plurality of first-type charged pigment particles and a plurality of second-type pigment particles. The electrophoretic medium may also contain a plurality of third-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fourth-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fifth-type charged pigment particles. Typically, the multiple microcapsules are retained within a polymer adhesive 132. A viewer can view an image of the display 100 from a viewing side 150. At least one type of charged pigment particle may contain organic pigments. The colored electro-optic material layer 100 may be formed of a front panel laminate, as described in the background of the invention.

[0101] Another example of a color electro-optical display is Figure 2 As shown. Figure 2 The illustration shows a side view of an example of the basic structure of a portion of a color electro-optic display with microcapsules. The electro-optic display 200 has a viewing side 150. It sequentially includes: a first electrode layer 101 including light-transmitting electrodes, a second adhesive layer 105, an electro-optic material layer 102, a first adhesive layer 104, and a second electrode layer 103 including a plurality of pixel electrodes. The second adhesive layer 105 connects the first electrode layer 101 to the electro-optic material layer 102. The first adhesive layer 104 connects the electro-optic material layer 102 to the second electrode layer. The electro-optic material layer 102 includes a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and includes an electrophoretic medium 122, which contains charged pigment particles and a charge control agent in a non-polar liquid. The electrophoretic medium 122 includes a plurality of first-type charged pigment particles and a plurality of second-type pigment particles. The electrophoretic medium may also contain a plurality of third-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fourth-type charged pigment particles. The electrophoretic medium 122 may also contain a plurality of fifth-type charged pigment particles. At least one type of charged pigment particle may contain organic pigments. Typically, multiple microcapsules are retained within the polymer binder 132. A viewer can view the image of the display 200 from the viewing side 250. The colored electro-optic material layer 100 may be formed of a front panel laminate, as described in the background of the invention.

[0102] Figure 1 and Figure 2 The microencapsulated color electro-optic display may also include a light-transmitting front substrate ( Figure 1 and Figure 2 (Not shown in the image), the light-transmitting front substrate is adjacent to the first electrode layer 101, wherein the electrode layer is disposed between the front substrate and the electro-optic material layer (for...). Figure 1 (for the display) or between the front substrate and the second adhesive layer (for the display) Figure 1 The front substrate can be a plastic film, such as a polyethylene terephthalate (PET) sheet with a thickness of 25 to 200 μm. The front substrate may also include one or more additional layers, such as a protective layer that absorbs ultraviolet radiation, a barrier layer that prevents oxygen or moisture from entering the display, and an anti-reflective coating that improves the optical properties of the display.

[0103] Figure 3 The illustration shows an example of a color electro-optical display containing micro-units. Figure 3 The color electro-optic display 300 sequentially includes a first electrode layer 201, an electro-optic material layer 202, an adhesive layer 204, and a second electrode layer 203 including multiple pixel electrodes. The adhesive layer 204 connects the sealing layer 232 of the electro-optic material layer 202 to the second electrode layer 203. The electro-optic material layer 202 of the color electro-optic display 300 includes multiple microcells 212 and a sealing layer 232. Each microcell 212 has a bottom 242, a partition wall 252, and an opening, and the sealing layer 232 spans the opening of each microcell. Each microcell 212 includes an electrophoretic medium 222. The electrophoretic medium 222 includes multiple first-type charged pigment particles 272, multiple second-type charged pigment particles 262, and a charge control agent in a non-polar liquid. The electrophoretic medium 222 may also include multiple third-type charged pigment particles. The electrophoretic medium 222 may also contain multiple fourth-type charged pigment particles. The electrophoretic medium 222 may also contain a plurality of fifth-type charged pigment particles. At least one type of charged pigment particle may contain organic pigments. A viewer can view the image on the display 300 from the viewing side 350. The colored electro-optic material layer 300 may be formed of a front panel laminate, as described in the background of the invention. Figure 3 Micro-unit color electro-optic displays may also include a light-transmitting front substrate ( Figure 3 (Not shown in the image), the light-transmitting front substrate is adjacent to the first electrode layer 201, wherein the electrode layer is disposed between the front substrate and the electro-optic material layer. The front substrate may be a plastic film, such as a polyethylene terephthalate (PET) sheet with a thickness of 25 to 200 μm. The front substrate may also include one or more additional layers, such as a protective layer for absorbing ultraviolet radiation, a barrier layer for preventing oxygen or moisture from entering the display, and an anti-reflective coating for improving the optical properties of the display.

[0104] Figure 1 , 2The charge control agent for the electrophoretic media of the electrooptic displays 100, 200, and 300 of the three types has a molecular structure comprising a quaternary ammonium functional group or an imidazolium cation, a hydrophobic tail group, and a counter ion. The counter ion of the charge control agent is an anion, which is the conjugate base of an acid with a pKa less than or equal to -2.5, or between -2.5 and -16. The charge control agent can be represented by formula I, II, III, IV, or V, having the above-described limitations. The charge control agent can be a branched polyethyleneimine derivative as described above. The charge control agent can also be a molecule represented by formulas I to V, or formulas VI to XIII, having the above-described limitations.

[0105] exist Figure 1 , 2 In the electro-optical display of 3, the first electrode layer may be a conductive layer with a thin, continuous coating of a conductive material that has minimal inherent absorption of electromagnetic radiation in the visible spectrum range, such as indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), graphene, etc.

[0106] Microcells can be formed in batch or continuous roll-to-roll processes, as disclosed in U.S. Patent No. 6,933,098. The latter provides a continuous, low-cost, high-volume manufacturing technique for producing chambers for a variety of applications, including electro-optical display devices. Microcell arrays suitable for this invention can be fabricated using microimprinting. Example

[0107] Examples of preparation of charge control agents

[0108] Comparative Example 1 Castor oil acid was mixed with 3-(dimethylamino)-1-propylamine and heated to 210°C under nitrogen, with water removed by azeotropic distillation using toluene. After the reaction was determined to be complete by acid titration, the reaction mixture was cooled to room temperature. Then, dimethyl sulfate (one equivalent of an amine) was added as an alkylating agent, and the methylation reaction was allowed to proceed under ambient conditions for at least 12 hours. Upon completion of the reaction, excess toluene was removed by vacuum distillation, and the product was mixed with a specified solvent (e.g., IsoparE). The structure and preparation of Comparative Example 1 are described as CCA-111 in U.S. Patent Application Publication No. 2020 / 0355978. Figure 4 The diagram illustrates the methylation reaction, where R stands for poly(ricinoleic acid).

[0109] Example 2 Repeat the process of Comparative Example 1, using methyl trifluoromethanesulfonate instead of dimethyl sulfate as the methylating agent. Figure 5 The diagram illustrates the methylation reaction, where R stands for poly(ricinoleic acid).

[0110] I. Examples of preparing dispersions of pigment particles in Isopar E

[0111] Example 3 As described in Example 1 of U.S. Patent No. 8,582,196, white pigment particles were prepared using a titanium dioxide pigment core comprising a polymer coating. The polymer coating comprised lauryl methacrylate (LMA) and 2,2,2-trifluoroethyl methacrylate (TFEM) in a molar ratio of approximately 95:5.

[0112] Example 4 White pigment particles were prepared using a titanium dioxide pigment core containing a polymer coating formed from lauryl methacrylate monomer.

[0113] Example 5 As described in Example 1 of U.S. Patent No. 8,582,196, white pigment particles were prepared using a titanium dioxide pigment core comprising a polymer coating. The polymer coating comprised lauryl methacrylate (LMA) and 2,2,2-trifluoroethyl methacrylate (TFEM) in a molar ratio of approximately 99:1.

[0114] Example 6 Cyan pigment particles were prepared using a cyan copper phthalocyanine pigment (CI Pigment Blue 15:3) containing a polymer coating. The polymer coating was formed using methyl methacrylate monomer (MMA) and polysiloxane macromonomer (PDMS).

[0115] Example 7 Magenta pigment particles were prepared using a magenta dimethylquinacridone pigment (CI Pigment Blue 15:122) comprising a polymer coating. The polymer coating was formed using vinyl chloride benzyl (VBC) and lauryl methacrylate (LMA), as described in U.S. Patent No. 9,697,78.

[0116] Example 8 As generally described in U.S. Patent No. 9,697,778, a dispersion of yellow particles is prepared by grinding pigment yellow 155.

[0117] All pigment particles were used as pigment particle dispersions in Isopar E. Specifically, (a) white pigment particles from Example 3 were used to prepare a white pigment dispersion in Isopar E, corresponding to Example 3B; (b) white pigment particles from Example 4 were used to prepare a white pigment dispersion in Isopar E, corresponding to Example 4B; (c) white pigment particles from Example 5 were used to prepare a white pigment dispersion in Isopar E, corresponding to Example 5B; (d) cyan pigment particles from Example 6 were used to prepare a cyan pigment dispersion in Isopar E, corresponding to Example 6B; (e) magenta pigment particles from Example 7 were used to prepare a magenta pigment dispersion in Isopar E, corresponding to Example 7B; and (f) yellow pigment particles from Example 8 were used to prepare a yellow pigment dispersion in Isopar E, corresponding to Example 8B.

[0118] II. Preparation of electrophoretic media with a single type of pigment particles

[0119] Example 10 A series of electrophoretic media were prepared using a white dispersion from Example 3B and a charge control agent from Example 2. Each electrophoretic medium contained varying amounts of charge control agent and the same amount of white pigment particles. The weight ratio of the charge control agent (CCA) series to the white particles ranged from approximately 0.2 mg to approximately 150 mg of CCA per gram of white pigment. The zeta potential of the pigment in each electrophoretic medium was determined, with the maximum zeta potential determined when it was positive and the minimum zeta potential determined when it was negative. In Example 10, the minimum zeta potential was determined to be -11.2 eV.

[0120] Example 11 The process of Example 10 was repeated to prepare a series of electrophoretic media using a white dispersion from Example 4B and a charge control agent from Example 2. In Example 11, the maximum zeta potential was 38.6 eV.

[0121] Example 12 The process of Example 10 was repeated to prepare a series of electrophoretic media using a white dispersion from Example 5B and a charge control agent from Example 2. In Example 12, the maximum zeta potential was -20.6 eV.

[0122] Comparative Example 13 The process of Example 10 was repeated to prepare a series of electrophoretic media using a white dispersion from Example 3B and a charge control agent from Comparative Example 1. In Comparative Example 13, the minimum zeta potential was -42.2 eV.

[0123] Comparative Example 14The process of Example 10 was repeated to prepare a series of electrophoretic media using a white dispersion from Example 4B and a charge control agent from Comparative Example 1. In Comparative Example 14, the minimum zeta potential was -24.1 eV.

[0124] Comparative Example 15 The process of Example 10 was repeated to prepare a series of electrophoretic media using a white dispersion from Example 5B and a charge control agent from Comparative Example 1. In Comparative Example 13, the minimum zeta potential was -62.3 eV.

[0125] Example 16 The process of Example 10 was repeated to prepare a series of electrophoretic media using the cyan dispersion from Example 6B and the charge control agent from Example 2. In Example 16, the minimum zeta potential was 75.6 eV.

[0126] Example 17 The process of Example 10 was repeated to prepare a series of electrophoretic media using a magenta dispersion from Example 7B and a charge control agent from Example 2. In Example 17, the maximum zeta potential was 58.4 eV.

[0127] Example 18 The process of Example 10 was repeated to prepare a series of electrophoretic media using the yellow dispersion from Example 8B and the charge control agent from Example 2. In Example 18, the minimum zeta potential was -20.4 eV.

[0128] Comparative Example 19 The process of Example 10 was repeated to prepare a series of electrophoretic media using the cyan dispersion from Example 6B and the charge control agent from Comparative Example 1. In Example 19, the maximum zeta potential was 70.0 eV.

[0129] Comparative Example 20 The process of Example 10 was repeated to prepare a series of electrophoretic media using a magenta dispersion from Example 7B and a charge control agent from Comparative Example 1. In Example 20, the maximum zeta potential was 56.0 eV.

[0130] Comparative Example 21 The process of Example 10 was repeated to prepare a series of electrophoretic media using the yellow dispersion from Example 8B and the charge control agent from Comparative Example 1. In Example 21, the minimum zeta potential was -25.2 eV.

[0131] The results of the measurement of the maximum particle zeta potential of charged particles in Examples 10-12, 13-15 and Comparative Examples 13-15, 19-21 are shown in Table 1 and . Figure 6 middle. Figure 6 The black bar corresponds to the comparison, while Figure 6The white bars in the diagram correspond to the black bars.

[0132] Table 1 ζ: The maximum zeta potential of various electrophoretic charged particles in the electrophoretic medium.

[0133]

[0134] Table 1 and Figure 6 The zeta potential data of the medium-white charged pigment particles (Examples 1-12 and Comparative Examples 13-15) show that the charge control agent (CCA) of the present invention from Example 2 interacts differently with the pigment particle type compared to the comparative CCA, depending on the surface properties of the particle type. Specifically, as Figure 6 As seen, the CCA of the present invention from Example 2 provides white particles with a zeta potential (negative or positive), which is significantly less negative (or even positive) than the zeta potential of the same white particles in the presence of the comparative CCA from Example 1. That is, the zeta potentials of the particles in Examples 10 and 12 of the present invention are much less negative than the zeta potentials of the particles in Comparative Examples 13 and 15, even though they contain the same electrophoretic particles (from Examples 3 and 5, respectively). Similarly, although Examples 11 and 14 contain the same electrophoretic particles from Example 4, the zeta potential of the particles in Example 11 of the present invention is positive compared to the negative zeta potential of the particles in Comparative Example 14. On the other hand, the CCA of the present invention and the comparative CCA provide a medium containing particles having zeta potentials very similar to those of particles in the other three charged particle types (cyan, magenta, and yellow), such as... Figure 6 As shown (the zeta potentials of Examples 16, 17, and 18 are relative to the zeta potentials of Comparative Examples 19, 20, and 21, respectively). That is, the present invention provides a useful tool for those skilled in the art to design electrophoretic media by selecting the CCA of the present invention, which has a desired zeta potential for one type of charged particle without affecting the zeta potential of other types of charged particles. This allows for better control over the electro-optical performance of the corresponding electro-optic display. In the embodiments presented above, the surfaces of all white particles are acidic, while the surfaces of yellow, cyan, and yellow particles are less acidic, neutral, or alkaline. Given that those skilled in the art can select appropriate particle surface acidity / alkalinity for various charged particles in the electrophoretic medium, it is evident that the CCA of the present invention can improve the electro-optical performance of various electrophoretic systems.

[0135] Measurement of the zeta potential of charged pigment particles

[0136] The zeta potential of pigment particles from the electrophoretic media of Examples 10, 11, 12, 16, 17, 18 and Comparative Examples 13, 14, 15, 19, 20 and 21 was measured using Colloidal Dynamics AcoustoSizer II and ZetaProbe. Figure 6 The results for the maximum values ​​for each type of charged particle are provided in the figure and Table 1.

[0137] III. Preparation of electrophoretic media and electro-optic displays with various types of pigment particles

[0138] Example 22

[0139] Electrophoretic media were prepared using charged particle dispersions from Examples 3B, 6B, 7B, and 8B, and a charge control agent from Example 2. Electrophoretic media were then used to prepare… Figure 3 The electro-optical display illustrated in the figure.

[0140] Comparative Example 23

[0141] Electrophoretic media were prepared using charged particle dispersions from Examples 3B, 6B, 7B, and 8B, and a charge control agent from Comparative Example 1. Electrophoretic media were then used to prepare… Figure 3 The electro-optical display illustrated in the figure.

[0142] Table 2 The color gamut of the present invention and the control electrophoresis display

[0143] Example number CCA source <![CDATA[Color gamut 0 o C]]> <![CDATA[Color gamut 25 o C]]> <![CDATA[Color gamut 50 o C]]> Example 22 Example 2 22603 36535 23314 Comparative Example 23 Comparative Example 1 16621 24767 9300

[0144] Measurement of color gamut of electro-optic displays

[0145] Each electro-optic display from Example 22 and Comparative Example 23 was electrically driven to generate various optical states, and its reflectance spectrum was acquired using a spectrophotometer. For the yellow, red, magenta, blue, cyan, and green states, the CIE L*, a*, and b* values ​​of the reflected light from each electrophoretic display were measured. For each spectral sample, the minimum distance in L*a*b* space between the display color and each SNAP (Newspaper Advertising Production Specification) color standard primary color was calculated in ΔE* units. The full color gamut was also extracted for all measurement points. The smaller the distance, the closer the performance of the electrophoretic display is to the SNAP target, indicating better color saturation of the display's optical states. The color gamut of the electro-optic displays from Example 22 and Comparative Example 23 was measured at three different temperatures (0°C, 25°C, and 50°C). The color gamut results at the three temperatures are summarized in Table 2 and Table 3, respectively. Figure 7 , 8In Figure 9, the solid lines correspond to the color gamut of the electro-optic display including an electrophoretic medium having the charge control agent of the present invention from Example 2. The short dashed lines correspond to the color standard (SNAP), and the long dashed lines correspond to the color gamut of the electro-optic display including an electrophoretic medium having the comparative charge control agent from Comparative Example 1.

[0146] From the color gamut values ​​in Table 2 and Figure 7-9 The conclusion drawn from the graphs is that the charge control agent of the present invention provides a wider color gamut for electro-optic displays having an electrophoretic medium containing the charge control agent, the molecular structure of which comprises (1) a quaternary ammonium functional group or an imidazolium cation, (2) a hydrophobic tail group, and (3) a counter ion, wherein the counter ion of the charge control agent is an anion that is the conjugate base of an acid with a pKa less than or equal to -2.5. Furthermore, an improved color gamut was observed over a wide temperature range (0°C to 50°C).

Claims

1. An electrophoretic medium comprising a plurality of charged particles, a charge control agent, and a nonpolar liquid, wherein the charge control agent has a molecular structure comprising a quaternary ammonium functional group or an imidazolium cation, a hydrophobic tail group, and a counter ion, wherein the counter ion of the charge control agent is an anion, the anion being a conjugate base of an acid having a pKa less than or equal to -2.5, wherein the plurality of charged particles are capable of moving through the nonpolar liquid when an electric field is applied.

2. The electrophoretic medium of claim 1, wherein the counter ion of the charge control agent is an anion, the anion is the conjugate base of an acid, and the acid has a pKa of -2.5 to -16.

3. The electrophoretic medium of claim 1, wherein the counter ion of the quaternary ammonium functional group or the counter ion of the imidazolium cation is selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide and iodide.

4. The electrophoretic medium according to any one of claims 1 to 3, wherein the weight-average molecular weight of the charge control agent is greater than or equal to 1000 g / mol.

5. The electrophoretic medium according to any one of claims 1 to 4, wherein the charge control agent is a molecule selected from branched polyethyleneimine derivatives, molecules represented by formula I, molecules represented by formula II, molecules represented by formula III, molecules represented by formula IV, and molecules represented by formula V. in, The branched polyethyleneimine derivative has a molecular structure comprising one or more quaternary ammonium functional groups and one or more hydrophobic moieties. R1 is independently selected from aryl groups and alkyl groups, wherein the alkyl group has 1 to 10 carbon atoms; m is an integer from 0 to 3; Z is one of the branched or unbranched alkyl diyl groups; n is an integer from 3 to 20; Q is a fraction selected from esters, thioesters, amides, imides, ureas, and carbamates; R2 is the hydrophobic component; R3, R4 and R5 are selected from alkyl groups and aryl groups having 1 to 20 carbon atoms; Each R6 and R7 is independently selected from alkyl groups, aryl groups, and -(Z) groups having 1 to 20 carbon atoms. n -Q-R2, and at least one of R6 and R7 is -(Z). n -Q-R2; and Y- is a counter ion.

6. The electrophoretic medium of claim 5, wherein the hydrophobic portion of the branched polyethyleneimine derivative and the hydrophobic portion R2 of formulas I to V are selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof.

7. The electrophoretic medium according to claim 5 or claim 6, wherein the hydrophobic portion R2 of formula I to V has 50 to 1000 carbon atoms or 10 to 300 dimethylsiloxane groups.

8. The electrophoretic medium according to any one of claims 5 to 7, wherein the hydrophobic portion of the branched polyethyleneimine derivative and the hydrophobic portion R2 of formulas I to V are derived from monomers selected from castor oil acid, isobutylene, hydroxystearic acid and combinations thereof.

9. The electrophoretic medium according to any one of claims 5, 6, and 8, wherein the charge control agent is a branched polyethyleneimine derivative having more than one hydrophobic moiety and one or more quaternary ammonium functional groups, wherein the branched polyethyleneimine derivative is formed from a branched polyethyleneimine having primary, secondary, and tertiary amine functional groups, wherein the more than one hydrophobic moiety of the branched polyethyleneimine derivative is formed by reacting the primary and / or secondary amine groups with monomers selected from castor oil, isobutylene, hydroxystearic acid, and combinations thereof, and wherein the more than one quaternary ammonium functional group of the branched polyethyleneimine derivative is formed by alkylation of the tertiary amine functional group of the branched polyethyleneimine.

10. The electrophoretic medium according to any one of claims 5, 6, 8 and 9, wherein the counter ion of the quaternary ammonium functional group of the branched polyethyleneimine derivative is selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide and iodide.

11. The electrophoretic medium according to any one of claims 5, 6, 8, 9 and 10, wherein the branched polyethyleneimine derivative has a number-average molecular weight greater than 1000 g / mole.

12. The electrophoretic medium of claim 5, wherein the charge control agent is a molecule represented by formula VI or formula VII; in, Each R8, R9, R 10 The group is independently selected from alkyl groups, said alkyl groups having 1 to 10 carbon atoms; Where o is an integer from 3 to 10; Among them, R 11 The hydrophobic portion is selected from alkyl groups, alkenyl groups, polyesters, polyethers, polyamides, polyurethanes, polyureas, polyacrylates, methacrylates, polydimethylsiloxanes, and combinations thereof; and The counterions are selected from trifluoromethanesulfonate, bis(trifluoromethane)sulfonamide, sulfate, perchlorate, chloride, bromide and iodide.

13. The electrophoretic medium of claim 12, wherein R8, R9, and R of formulas VI and VII are... 10 It is a methyl group, and the hydrophobic portion R of formulas VI and VII is... 11 It contains functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene).

14. The electrophoretic medium of claim 12, wherein the charge control agent is a molecule represented by formula VIII or formula IX. in, R 11 It is a hydrophobic portion containing a functional group selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene), wherein the counterion is trifluoromethanesulfonate.

15. The electrophoretic medium of claim 5, wherein the charge control agent is a molecule represented by formula X or formula XI; in, R 12 and R 13 It is a hydrophobic portion containing functional groups selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene), wherein the counterion is trifluoromethanesulfonate.

16. The electrophoretic medium of claim 5, wherein the charge control agent is a molecule represented by formula XII. in, R 14 The alkyl group is an alkyl group having 1 to 10 carbon atoms, and wherein R is an alkyl group. 15 It is a hydrophobic portion containing a functional group selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene), wherein the counterion is trifluoromethanesulfonate.

17. The electrophoretic medium of claim 5, wherein the charge control agent is a molecule represented by formula XIII. in, Each R 16 R 17 R 18 Independently selected from alkyl groups, said alkyl group having 1 to 10 carbon atoms, and wherein R 19 It is a hydrophobic portion containing a functional group selected from poly(hydroxystearic acid), poly(ricinoleic acid), and poly(isobutylene), wherein the counterion is trifluoromethanesulfonate.

18. The electrophoretic medium according to any one of claims 1 to 17, further comprising a second charge control agent, wherein the second charge control agent comprises a hydrophobic portion and a head group, the head group being selected from anionic, nonionic, and cationic functional groups.

19. The electrophoretic medium of claim 18, wherein the head group of the second charge control agent comprises an ammonium cation or an acyclic secondary amide group.

20. An electro-optic display comprising a first electrode layer, an electro-optic material layer, and a second electrode layer, wherein the first electrode layer is light-transmitting, the second electrode layer includes a plurality of pixel electrodes, the electro-optic material layer includes a plurality of microcapsules or a plurality of microunits, each microcapsule or microunit containing an electrophoretic medium according to any one of claims 1 to 19, wherein the electro-optic material layer is disposed between the first electrode layer and the second electrode layer, and wherein the first electrode layer and the second electrode layer are configured to apply an electric field across the electro-optic material layer.

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