Electrophoretic core-shell particles having an organic pigment core and a shell with a thin metal oxide layer and a silane layer

Abstract

An electrophoretic medium includes a plurality of core-shell particles and a non-polar fluid. The core-shell particles include an organic pigment particle core and a shell including a metal oxide layer and a silane layer. The metal oxide layer can have a thickness of 0.4 to 2 nm. It can be formed using a fluidized bed reactor by inserting an organic pigment into the reactor in the form of a powder bed, contacting the powder bed with a gas stream including a metal oxide precursor and an inert gas, and contacting the powder bed with a gas stream of a reagent and an inert gas. The silane layer is formed from a silane compound including a first functional group, where the first functional group reacts with the metal oxide.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and interest in U.S. Provisional Application No. 62 / 970,901, filed on February 6, 2020, the contents of which are incorporated herein by reference in their entirety. Invention Field

[0003] This invention relates to organic pigments for electrophoretic display media. More specifically, in one aspect, the invention relates to an electrophoretic system containing core-shell organic pigment particles having a shell comprising a thin metal oxide layer and a silane layer. Background of the Invention

[0005] This invention relates to particles for electrophoretic displays, and to electrophoretic media and displays incorporating such particles. More specifically, this invention relates to an electrophoretic media comprising a plurality of core-shell particles and a nonpolar liquid. In one aspect, the core-shell particles comprise (a) a core containing an organic pigment and (b) a shell comprising a metal oxide layer and a silane layer, wherein the metal oxide layer is formed by depositing the metal oxide onto the surface of the organic pigment using a fluidized bed reactor.

[0006] The term "electro-optic," when applied to materials or displays, is used herein in its conventional sense in imaging technology to refer to a material having a first display state and a second display state that differ in at least one optical property, which the material changes from its first display state to its second display state by applying an electric field. While this optical property is generally color perceptible to the human eye, it can also be another optical property such as optical transmission, reflection, emission, or, in the case of a display intended for machine reading, pseudo-color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible range.

[0007] Some electro-optic materials are solid in the sense that they have a solid outer surface, although the material may and often does indeed have internal spaces filled with liquid or gas. In the following text, for convenience, such a display using solid electro-optic materials may be referred to as a "solid-state electro-optic display." Therefore, the term "solid-state electro-optic display" includes rotating dual-color component displays, encapsulated electrophoretic displays, microporous electrophoretic displays, and encapsulated liquid crystal displays.

[0008] The terms “bistable” and “bistable” are used herein in their conventional sense in the art to refer to a display comprising display elements having a first display state and a second display state that differ in at least one optical property, such that after any given element has been driven to present its first or second display state by means of an addressing pulse of finite duration, that state will persist after the addressing pulse terminates for at least several times, for example, at least four times, the minimum duration of the addressing pulse required to change the state of the display element. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays with grayscale capability are stable not only in their extreme black and white states but also in their intermediate gray states, and so are some other types of electro-optical displays. This type of display is properly referred to as “multistable” rather than bistable, but for convenience, the term “bistable” may be used herein to encompass both bistable and multistable displays.

[0009] One type of electro-optic display that has been the subject of intensive research and development for several years is the particle-based electrophoretic display, in which multiple charged particles move through a fluid under the influence of an electric field. Compared to liquid crystal displays (LCDs), electrophoretic displays offer advantages such as good brightness and contrast, wide viewing angles, state bistability, and low power consumption. However, issues concerning the long-term image quality of these displays have hindered their widespread use. For example, the particles constituting an electrophoretic display are prone to settling, leading to a short lifespan for these displays.

[0010] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but electrophoretic media can be prepared using a gaseous fluid; for example, see Kitamura, T. et al., “Electrical toner movement for electronic paper-like display,” IDW Japan, 2001, Paper HCS1-1, and Yamaguchi, Y. et al., “Toner display using insulative particles charged triboelectrically,” IDW Japan, 2001, Paper AMD4-4. See also U.S. Patents 7,321,459 and 7,236,291. When the medium is used in a direction that allows particle settling, such as when it is used in markings where the medium is positioned in a vertical plane, this gas-based electrophoretic medium appears to be susceptible to the same type of problems caused by particle settling as liquid-based electrophoretic media. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoresis media than in liquid-based electrophoresis media, because the lower viscosity of gaseous suspensions allows for faster sedimentation of electrophoretic particles compared to liquid electrophoresis media.

[0011] Numerous patents and applications assigned to or registered in the name of MIT, E Ink, E Ink California, LLC, and related companies describe various techniques for encapsulating electrophoretic media and microporous electrophoretic media, as well as other electro-optic media. The encapsulated electrophoretic media comprises numerous small capsules, each capsule itself including an inner phase containing electrophoretically moving particles in a fluid medium and a capsule wall surrounding the inner phase. Typically, the capsules themselves are held in a polymer binder to form a coherent layer located between two electrodes. In microporous electrophoretic displays, charged particles and fluid are not encapsulated within microcapsules but are retained within multiple cavities formed within a carrier medium, typically a polymer film. The techniques described in these patents and applications include:

[0012] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent Nos. 6,822,782; 7,002,728; 7,679,814; 8,018,640; 8,199,395; and 9,372,380; and U.S. Patent Application Publication No. US2018 / 0210312;

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

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

[0015] (d) Methods for filling and sealing micropores; 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) Backplane, adhesive layer and other auxiliary layers and methods for display; 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;

[0021] (j) Non-electrophoretic displays, as described in U.S. Patents Nos. 6,241,921 and 2015 / 0277160; and applications of encapsulation and microvia technologies other than displays; see, for example, U.S. Patent Application Publications Nos. 2015 / 0005720 and 2016 / 0012710.

[0022] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing a so-called polymer-dispersed electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete electrophoretic fluid droplets and a continuous phase of polymeric material, and the discrete electrophoretic fluid droplets within such a polymer-dispersed electrophoretic display can be considered as capsules or microcapsules even without a discrete membrane associated with each individual droplet; see, for example, the aforementioned U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, such a polymer-dispersed electrophoretic medium is considered a subtype of encapsulated electrophoretic medium.

[0023] Although electrophoretic media are often opaque (because, for example, in many electrophoretic media, particles essentially block the transmission of visible light through the display) and operate in reflective mode, many electrophoretic displays can operate in a so-called "shutter mode," in which one display state is substantially opaque and another display state 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. Dielectrophoretic 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 can also operate in shutter mode. In the multi-layered structure of a full-color display, an electro-optic medium operating in shutter mode may be useful; in such a structure, 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.

[0024] Encapsulated electrophoretic displays generally do not suffer from the aggregation and sedimentation failure modes of conventional electrophoresis devices and offer further advantages such as the ability to print or coat displays on a variety of flexible and rigid substrates. The term "printing" is intended to encompass all forms of printing and coating, including but not limited to: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, and screen coating; roll coatings such as knife-over roll coating and forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing methods; electrostatic printing methods; thermal printing methods; inkjet printing methods; 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 itself can be manufactured inexpensively.

[0025] However, the lifespan of encapsulated electrophoretic displays remains below full expectations. This lifespan appears to be limited by factors such as the tendency of particles to agglomerate, preventing them from completing the movements necessary for the display to switch between its optical states. The physical properties and surface characteristics of electrophoretic particles can be modified by adsorbing various materials onto the particle surface or chemically bonding various materials to these surfaces. For example, in electrophoretic displays containing organic pigments, monomers with different chemical groups can be dispersed and polymerized on the pigment to form polymer coatings, and these coatings can interact with charge control agents to provide colored particles with different charge intensities. A similar approach to achieving improved electro-optic performance is the use of organic pigment particles coated with metal oxides such as silica. Silica coatings enable other materials to covalently attach to the surface of the pigment particles, creating stable, differentiated surfaces between different types of electrophoretic particles in the medium. A general method for depositing silica onto organic pigment particles involves reacting hydrolyzable silicone materials such as triethoxysilane with water in an organic solvent and in the presence of organic pigment particles. If the process conditions are not strictly controlled, the coating will be uneven, with some areas uncovered and others covered with a thicker silica coating. This can lead to less efficient particle separation and a deterioration in the color properties of organic pigments. Therefore, there is a need for improved electrophoretic particles and their preparation methods. Invention Overview

[0027] According to one aspect of the invention, the electrophoretic medium comprises a plurality of first-type core-shell particles and a nonpolar fluid. Each of the plurality of first-type core-shell particles comprises a core and a shell containing an organic pigment. The shell comprises a metal oxide layer and a silane layer. The thickness of the metal oxide layer is from about 0.4 nm to about 2 nm. The silane layer is formed of a silane compound comprising a first functional group, wherein the first functional group reacts with the metal oxide. The electrophoretic medium may further comprise a plurality of second-type core-shell particles or another type of charged electrophoretic particles. The electrophoretic medium may also comprise more than two types of core-shell particles or other types of charged electrophoretic particles. The electrophoretic medium can be used in an electrophoresis apparatus comprising a first transparent electrode layer, an electro-optic material layer, and a second electrode layer. The electro-optic material layer of the electrophoresis apparatus comprises an encapsulated electrophoretic medium, i.e., microcapsules or micropores containing particles in a fluid. The electrophoretic medium can also be used in electrophoresis components such as front-plane laminates, inverted front-plane laminates, and dual-release sheets.

[0028] According to another aspect of the invention, the electrophoretic medium comprises a plurality of first-type core-shell particles and a nonpolar fluid. Each of the plurality of first-type core-shell particles comprises a core and a shell containing an organic pigment. The shell comprises a metal oxide layer and a silane layer. The metal oxide layer is formed on the surface of the organic pigment using a fluidized bed reactor by inserting the organic pigment into a reactor in the form of a powder bed, contacting the powder bed with a gaseous stream containing an inert gas and a metal oxide precursor, and contacting the powder bed with a gaseous stream of an inert gas and a reagent that reacts with the metal oxide precursor to form a metal oxide. The electrophoretic medium may further comprise a plurality of second-type core-shell particles or another type of charged electrophoretic particles. The electrophoretic medium may also comprise more than two types of core-shell particles or other types of charged electrophoretic particles. This electrophoretic medium can be used in an electrophoresis apparatus comprising a first transparent electrode layer, an electro-optic material layer, and a second electrode layer. The electro-optic material layer of the electrophoresis apparatus comprises an encapsulated electrophoretic medium, i.e., microcapsules or micropores containing particles in a fluid. The electrophoretic medium can also be used in electrophoresis components such as front-plane laminates, inverted front-plane laminates, and dual-release sheets.

[0029] According to another aspect of the invention, the shell of the core-shell particle further comprises a polymer stabilizer layer. This polymer stabilizer layer may be formed by the reaction of a silane layer and a monomer or macromonomer, wherein the silane compound used to form the silane layer contains a third functional group, and the monomer or macromonomer contains a fourth functional group. The polymer stabilizer layer is formed by the reaction between the third and fourth functional groups.

[0030] According to another aspect of the invention, a method for manufacturing an electrophoretic medium comprising a plurality of core-shell particles and a nonpolar fluid includes the following steps: (a) providing organic pigment particles; (b) introducing the organic pigment particles into a fluidized bed reactor in the form of a powder bed; (c) contacting the powder bed with a gaseous stream comprising an inert gas and a metal oxide precursor; (d) contacting the powder bed with a gaseous stream comprising a reagent to form organic pigment particles having a metal oxide layer on their surface, wherein the reagent is selected from water, oxygen, ozone, and mixtures thereof; (e) reacting the organic pigment particles having the metal oxide layer with a silane compound in an organic solvent to form a silane layer, wherein the silane compound comprises a first functional group and a third functional group, wherein the first functional group reacts with the metal oxide to form organic pigment particles comprising a metal oxide layer and a silane layer; and (f) combining the plurality of core-shell particles with the nonpolar fluid. The gaseous stream containing the reagent may further comprise an inert gas. Brief description of the attached diagram

[0032] Various aspects and embodiments of this application will be described with reference to the following figures. It should be understood that the figures are not necessarily drawn to scale.

[0033] Figure 1A This demonstrates a reaction scheme for forming core-shell particles that contain an organic pigment core and a shell with a metal oxide layer. Figure 1B This demonstrates a reaction scheme for forming core-shell particles, which consist of an organic pigment particle core and a shell containing a metal oxide layer and a silane layer. Figure 1C This illustrates a reaction scheme for forming core-shell particles that consist of an organic pigment particle core and a shell containing a metal oxide layer, a silane layer, and a polymer stabilizer layer.

[0034] Figure 2 This is a schematic diagram of an electrophoresis apparatus containing an electro-optic material layer with encapsulated electrophoretic medium.

[0035] Figure 3 This is a schematic diagram of an electro-optic component, which includes a first light-transmitting layer, an electro-optic material layer containing an encapsulated electrophoretic medium, an adhesive layer, and a front-plane laminate of a release sheet.

[0036] Figure 4 This is a schematic diagram of an electro-optic component, which is a dual-release sheet, comprising a first release sheet, a first adhesive layer, an electro-optic material layer containing an encapsulated electrophoretic medium, a second adhesive layer, and a second release sheet.

[0037] Figure 5 This demonstrates a reaction scheme for forming core-shell particles that include organic pigment particles and a shell containing a metal oxide layer, a silane layer, and a polymer stabilizer layer.

[0038] Detailed Explanation

[0039] This invention provides an electrophoretic medium comprising a plurality of core-shell particles and a nonpolar fluid. The core-shell particles comprise an organic pigment core and a shell comprising a metal oxide layer and a silane layer. The shell may also comprise a polymer stabilizer layer. This layer, if present, is located on the surface of the core-shell particles and contributes to the dispersion stability of the particles in the electrophoretic medium.

[0040] The electrophoretic medium of this invention can be incorporated into electro-optic displays. A typical electro-optic display containing the electrophoretic medium also includes a first (front) electrode and a second (rear) electrode. The first electrode is transparent. The second electrode may also be transparent, or it may be opaque. The electrophoretic medium, containing multiple charged particles in a non-polar fluid, is generally located between the front and rear electrodes.

[0041] Electrophoretic media can contain one or more types of particles that can have different colors and charges. For example, there are commercial electro-optic displays that contain electrophoretic media with white and black particles having opposite charges. However, there are also displays on the market that contain one or more types of charged organic particles. Organic pigments are preferred because they provide brighter and more saturated colors compared to inorganic pigments. Common organic pigments used in electro-optic displays may be cyan, magenta, yellow, red, green, blue, and black. Non-limiting examples of organic pigment types include azo, phthalocyanine, quinacridone, perylene, diketopyrrolopyrrole, benzimidazolone, isoindoline, anthrone, indanone, rhodamine, aniline, and carbon black. Although many practitioners consider carbon black pigment to be an inorganic pigment, for the purposes of this patent application, this type of pigment is considered an organic pigment because some of its physical properties, such as hydrophobicity and surface area, are similar to those of organic pigments. Non-limiting examples of specific organic pigments that can be used as electrophoretic media include CI Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 60, and 79; Pigment Red 2, 4, 5, 9, 12, 14, 38, 48:2, 48:3, 48:4, 52:2, 53:1, 57:1, 81, 112, 122, 144, 146, 147, 149, 168, 170, 176, 177, 179, 184, 185, 187, 188, 208, 209, 210, 214, 242, 254, 255, 257, 262, 264, 282, and 285; CI Pigments Violet 1, 19, 23 and 32; CI Pigments Yellow 1, 3, 12, 13, 14, 15, 16, 17, 73, 74, 81, 83, 97, 109, 110, 111, 120, 126, 127, 137, 138, 139, 150, 151, 154, 155, 174, 175, 176, 180, 181, 184, 191, 194, 213 and 214; CI Pigments Green 7 and 36; CI Pigments Black 1 and 7; CI Pigments Brown 25, 32, 41; Pigments Orange 5, 13, 34, 36, 38, 43, 61, 62, 64, 68, 67, 72, 73 and 74.

[0042] The average diameter of the organic pigment in the core of the core-shell particles of the present invention can be from 1 nm to a maximum of about 100 μm, or from 50 nm to 1 μm, or from 60 nm to 800 nm.

[0043] Organic pigments provide color because they absorb incident light at specific wavelengths corresponding to visible light. Generally, their color saturation and intensity increase with decreasing particle size (i.e., with increasing surface area). Therefore, they are mostly obtained in particle form with relatively high surface areas, making them relatively difficult to disperse and stabilize in liquid carriers.

[0044] According to one embodiment of the invention, the electrophoretic medium comprises a plurality of core-shell particles of type 1 and a nonpolar fluid. The core comprises an organic pigment, while the shell comprises a metal oxide layer and a silane layer.

[0045] The metal oxide layer is formed on the surface of the organic pigment by inserting an organic pigment into a reactor in the form of a powder bed, contacting the powder bed with a gaseous stream containing an inert gas and a metal oxide precursor, and then contacting the powder bed with a gaseous stream containing an inert gas and a reagent. The reagent reacts with the metal oxide precursor to form the metal oxide.

[0046] Fluidized bed reactors can be used in continuous or batch processes. A typical fluidized bed reactor comprises a chamber that tightly mixes the powder material with a gaseous reagent to improve both reaction rate and the uniformity of the modified powder surface. The pigment powder can be placed vertically on a porous plate in the form of a powder bed within the reactor. A gaseous stream of metal oxide precursor / inert gas can be injected from an inlet at the top or bottom of the reactor chamber. For example, a trimethylaluminum gaseous stream in nitrogen can be used. The bed can be continuously vibrated. Additionally, the gas pressure may decrease due to resistance from the powder bed, which may also lead to continuous movement of the powder and suspension of the powder in the gaseous stream, improving the contact between the powder surface and the reagent. The metal oxide precursor can be complexed (or adsorbed) onto the powder surface in the form of a thin layer. The gaseous stream can then be changed from the metal oxide precursor to a reagent / inert gas stream, such as water / nitrogen. This gaseous stream will cause the metal oxide precursor film to react with the reagent, forming a thin layer on the powder surface. In continuous methods using horizontal fluidized bed reactors, a powder bed can be continuously conveyed from one side of a chamber to the other, through separate zones where the powder is exposed to separate gaseous streams (metal oxide precursor / nitrogen stream, followed by reagent / nitrogen stream). It is possible to include separate gas streams before delivering the surface-treated powder from the outlet of the fluidized bed reactor, which may result in the removal of excess reagents, such as the drying of pigment powders. U.S. Patent Application No. US2018 / 0363136 of ALD Nanosolutions, Inc. provides an example of a continuous method.

[0047] Figure 1AThe diagram illustrates a reaction scheme for forming a metal oxide layer on the surface of organic pigment particles 101. A gaseous stream of a metal oxide precursor in an inert gas is brought into contact with a powder bed of organic pigment particles 101. The precursor is complexed or adsorbed onto the surface of the organic pigment particles, where it reacts with a subsequent gaseous stream of a reagent in an inert gas to form a metal oxide layer 102 with a thickness of L1. Then, as... Figure 1B As shown, particle 102 (an organic pigment particle having a metal oxide layer on its surface) reacts with silane compound 103. This silane has a substituent F1 containing a first functional group that can react with the metal oxide surface to provide core-shell particle 104. The core-shell particle 104 has a metal oxide layer of thickness L1 and a silane layer of thickness L2. The silicon atoms of the silane compound also have substituents R1, R2, and R3. One or both of these substituents may also be a substituent F1 containing a first functional group that can also react with the metal oxide surface. At least one of R1, R2, and R3 may contain a second functional group that can provide charge to the particle, or it may modify surface characteristics of the core-shell particle such as its surface energy.

[0048] The metal oxide layer may contain aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, zinc oxide, or mixtures thereof.

[0049] Non-limiting examples of metal oxide precursors are trimethylaluminum, triethylaluminum, dimethylaluminum chloride, diethylaluminum chloride, trimethoxyaluminum, triethoxyaluminum, dimethylaluminum propylene oxide, triisopropylaluminum oxide, tributoxyaluminum, tri(dimethylamino)aluminum, tri(diethylamino)aluminum, tri(propylamino)aluminum, aluminum trichloride, trichlorosilane, hexachlorodisilane, silicon tetrachloride, tetramethoxysilane, tetraethoxysilane, tri(tert-pentoxy)silanol, tetraisocyanate silane, silicon tetrachloride, tri(methylamino)silane, tri(ethylamino)silane, titanium tetrachloride, titanium tetraiodide, tetramethoxytitanium tetraethoxytitanium, titanium isopropylaluminum oxide, tetra(methylamino)titanium tetra(ethylamino)titanium, dimethylzinc, diethylzinc, methyl zinc isopropylaluminum oxide, zirconium tetrachloride, zirconium tetraiodide, zirconium tetramethoxy, zirconium tetraethoxy, zirconium tetraisopropylaluminum oxide, zirconium tetrabutoxy, zirconium tetra(methylamino), zirconium tetra(ethylamino) and mixtures thereof. These metal oxide precursors were supplied by Sigma-Aldrich.

[0050] Non-limiting examples of reagents are water, oxygen, ozone, and mixtures thereof.

[0051] The thickness of the metal oxide layer can range from about 0.4 nm to about 2 nm, or from about 0.5 nm to about 1 nm, or from about 0.5 nm to about 0.8 nm.

[0052] Non-limiting examples of the second functional group of a silane layer that can provide charge to core-shell particles or modify the surface features of core-shell particles are alkyl groups, haloalkyl groups, alkenyl groups, aryl groups, hydroxyl groups, carboxyl groups, sulfate ester groups, sulfonate ester groups, phosphate ester groups, phosphonic acid groups, amine groups, quaternary ammonium groups, dimethylsiloxane groups, ester groups, amide groups, and ethyleneimine groups.

[0053] Non-limiting examples of the first functional group of silane compounds that can react with metal oxide layers are alkoxy, alkylamino, halide, hydrogen, and hydroxyl groups. This means that the silicon atom of the silane can be attached to an alkoxy group, an alkylamino group, a halide group, a hydrogen group (Si-H), and a hydroxyl group, respectively.

[0054] An example of a class of silane compounds of metal oxides used for bonding to metal oxide layers is a trialkoxysilane coupling group, such as 3-(trimethoxysilyl)propyl methacrylate, commercially available from Dow Chemical Company, Wilmington, Del. under the trade name Z6030. The corresponding acrylates may also be used.

[0055] According to a second embodiment of the invention, the electrophoretic medium comprises core-shell particles and a nonpolar fluid, wherein the core comprises an organic pigment, and the shell comprises a metal oxide layer, a silane layer, and a polymer stabilizer layer. The metal oxide layer is formed on the surface of the organic pigment using a fluidized bed reactor. The silane compound used to form the silane layer may comprise a first functional group and a third functional group. The first functional group may react with the metal oxide layer to form the silane layer. The silane layer may then react via the third functional group with a monomer or macromonomer comprising a fourth functional group to form the polymer stabilizer layer.

[0056] Figure 1CThe diagram illustrates a series of reactions for the formation of core-shell particles 116, where the core comprises an organic pigment, and the shell comprises a metal oxide layer, a silane layer, and a polymer stabilizer layer. More specifically, particles 102 comprising a core (organic pigment 101) and a metal oxide layer of thickness L1 can react with a silane compound 113 comprising a substituent F1 having a first functional group and a substituent F3 having a third functional group. The first functional group can react with the metal oxide layer of particle 102 to form core-shell particles 114. The core of the core-shell particle comprises an organic pigment, and the shell comprises a metal oxide layer of thickness L1 and a silane layer of thickness L2. Particle 114 can react with a monomer (or macromonomer M1-F4) via the third functional group in substituent F2 to form core-shell particles 115, which comprises a shell having a metal oxide layer of thickness L1, a silane layer of thickness L2, and a polymer stabilizer layer of thickness L3. The polymer stabilizer layer is formed by the reaction of the third functional group in the silane substituent F3 with the fourth functional group F4 of the monomer or macromonomer M1-F4. Silane compound 113 also contains substituents R4 and R5. One or both of substituents R4 and R5 may also contain a first functional group capable of reacting with the metal oxide layer. Additionally, one or both of substituents R4 and R5 may also contain a third functional group capable of reacting with the fourth functional group of the monomer or macromonomer M1-F4.

[0057] According to a second embodiment of the invention, the polymer stabilizer layer may be formed by the reaction of one or more monomers or macromonomers having a fourth functional group with a polymerizable third functional group of a silane. Various polymerization techniques known to those skilled in the art, such as random graft polymerization (RGP), ionic random graft polymerization (IRGP), and atom transfer radical polymerization (ATRP), as described in U.S. Patent No. 6,822,782, the contents of which are incorporated herein by reference in their entirety. As used herein throughout the specification and claims, a macromonomer refers to a macromolecule having an end group that enables it to function as a monomer.

[0058] Suitable monomers for forming the polymer stabilizer layer may include, but are not limited to, styrene, α-methylstyrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, vinylpyridine, n-vinylpyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, and methacrylic acid. Octyl acrylate, octadecyl acrylate, octadecyl methacrylate, 2-perfluorobutyl ethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, and 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, etc. The macromonomer may contain terminal functional groups selected from acrylate groups, vinyl groups, or combinations thereof.

[0059] In one embodiment of the invention, a macromonomer or polymerizable monomer is attached to the surface of the particle via a reaction with a third functional group of the silane layer to form a polymer stabilizer layer. The third functional group can be epoxy, vinyl, styrene, acryloyl, methacryl, methacryloyloxyalkyl, amino, hydroxyl, carboxyl, alkoxy, or chloride. An example of a silane compound that can form the silane layer of the core-shell particle is 3-(trimethoxysilyl)propyl methacrylate, commercially available from Dow Chemical Company, Wilmington, Del under the trade name Z6030. Corresponding acrylates may also be used.

[0060] Other macromonomers and silane compounds that can be used to form core-shell particles are described in U.S. Patent Application No. 2018 / 0210312, the contents of which are incorporated herein by reference in their entirety.

[0061] One type of macromonomer that can be used to form the polymer stabilizer layer can be, for example, acrylate-terminated polysiloxanes such as Gelest, MCR-M11, MCR-M17, or MCR-M22. Another type of macromonomer suitable for this method is the PE-PEO macromonomer, as shown below:

[0062] R m O--[--CH2CH2O--] n --CH2-phenyl-CH=CH2; or

[0063] R mO--[--CH2CH2O--] n --C(=O)--C(CH3)=CH2.

[0064] The substituent R can be a polyethylene chain, n is 1-60, and m is 1-500. Synthesies of these compounds can be found in Dongri Chao et al., Polymer Journal, Vol. 23, No. 9, 1045 (1991) and Koichi Ito et al., Macromonomers, 1991, 24, 2348. Another suitable type of macromonomer is the PE macromonomer, as shown below:

[0065] CH3--[--CH2--] n --CH2O--C(=O)--C(CH3)=CH2.

[0066] In this case, n is 30-100. The synthesis of this type of macromonomer can be found in Seigou Kawaguchi et al., Designed Monomers and Polymers, 2000, 3, 263.

[0067] When choosing bifunctional compounds, such as silanes containing a first and a third functional group, to provide polymerizable or initiating functionality on particles, attention should be paid to the relative positions of these two groups in the reagent. As will be apparent to those skilled in the art of polymer preparation, the reaction rate of the polymerizable or initiating group bonded to the particle can vary considerably depending on whether the group is held rigidly close to the particle surface or whether the group is spaced apart from the surface (at the atomic scale) and thus extends into the reaction medium surrounding the particle, where the group is spaced apart from the surface (at the atomic scale) and thus extends into the reaction medium surrounding the particle, which is a much more favorable environment for the chemical reaction of the group. Generally, it is preferred that at least three atoms are present in the straight chain between the two functional groups; for example, the aforementioned 3-(trimethoxysilyl)propyl methacrylate provides a chain containing four carbon atoms and one oxygen atom between the silyl and olefinic unsaturated groups, while the aforementioned 4-vinylaniline separates the amino group (or diazo group, in the actual reactive form) from the vinyl group through the full width of the benzene ring, equivalent to about a three-carbon chain length.

[0068] In any of the methods described above, the amounts of the reagents used (e.g., organic core pigment particles, metal oxide layer materials, and materials for forming the polymer stabilizer layer) can be adjusted and controlled to achieve the desired organic content in the resulting core-shell particles. Furthermore, the methods of the present invention may include more than one stage and / or more than one type of polymerization.

[0069] As described above, the particles prepared according to various embodiments of the invention are dispersed in an encapsulation fluid. It is desirable that the polymer stabilizer layer is highly compatible with the encapsulation fluid. In practice, the suspension fluid in the electrophoretic medium is typically hydrocarbon-based, although the fluid may contain a proportion of halogenated hydrocarbons to increase the fluid density and thus reduce the difference between the fluid density and the particle density. Therefore, it is important that the polymer stabilizer layer formed in this method is highly compatible with the encapsulated fluid, and thus the polymer stabilizer layer itself contains a predominantly hydrocarbon chain; a large number of strong ionic groups, in addition to those provided for charging purposes, are undesirable as they make the material of the polymer stabilizer layer less soluble in the hydrocarbon suspension fluid and thus adversely affect the stability of the particle dispersion. Moreover, as already discussed, at least when the medium in which the particles are used contains an aliphatic hydrocarbon suspension fluid (generally), it is advantageous that the material of the polymer stabilizer layer has a branched or "comb-like" structure, having a main chain and multiple side chains extending away from the main chain. Each of these side chains should have at least about four, preferably at least about six carbon atoms. Longer side chains are generally advantageous; for example, some preferred materials for the polymer stabilizer layer may have lauroyl (C) groups. 12 Side chains. These side chains themselves can be branched; for example, each side chain can be a branched alkyl group such as a 2-ethylhexyl group. It is believed (although the invention is by no means limited to this view) that, due to the high affinity of the hydrocarbon chains for the hydrocarbon-based suspension, the branches of the polymer stabilizer layer material diffuse into each other in a brush-like or dendritic structure, penetrating a large amount of liquid, thereby increasing the affinity of the particles for the suspension and the stability of the particle dispersion.

[0070] There are two basic methods for forming this comb-like polymer. The first method uses monomers that inherently provide the necessary side chains. Generally, such monomers have a single polymerizable group at one end of a long chain (at least four, preferably at least six carbon atoms). Monomers of this type that have been found to produce good results in this method include hexyl acrylate, 2-ethylhexyl acrylate, and lauryl methacrylate. Isobutyl methacrylate and 2,2,3,4,4,4-hexafluorobutyl acrylate have also been successfully used. In some cases, it may be desirable to limit the number of side chains formed in this method, which can be achieved by using a mixture of monomers (e.g., a mixture of lauryl methacrylate and methyl methacrylate) to form a random copolymer, where only some repeating units have long side chains. In the second method, typically the RGP-ATRP method, a first polymerization reaction is carried out using a mixture of monomers, at least one of which has an initiating group, thereby producing a first polymer containing such an initiating group. The product of the first polymerization reaction is then subjected to a second polymerization, typically under different conditions, to allow the initiating groups within the polymer to induce the polymerization of additional monomers onto the original polymer, thereby forming the desired side chains. Similar to the bifunctional reagents discussed above, we do not rule out the possibility of some chemical modification of the initiating groups between the two polymerizations. In this method, the side chains themselves do not need to be highly branched and can be formed from small monomers such as methyl methacrylate.

[0071] Free radical polymerization of olefins or similar freely polymerizable groups attached to particles can be carried out at high reaction temperatures, preferably 60 to 70 °C, using conventional free radical initiators such as azobisisobutyronitrile (AIBN), while ATRP polymerization can be carried out using conventional metal complexes, as described in Wang, JS et al., Macromolecules 1995, 23, 7901, and J. Am. Chem. Soc. 1995, 117, 5614, and Beers, K. et al., Macromolecules 1999, 32, 5772-5776. See also U.S. Patents 5,763,548; 5,789,487; 5,807,937; 5,945,491; 4,986,015; 6,069,205; 6,071,980; 6,111,022; 6,121,371; 6,124,411; 6,137,012; 6,153,705; 6,162,882; 6,191,225; and 6,197,883. The entire disclosure of these documents and patents is incorporated herein by reference. Currently preferred catalysts for ATRP are cuprous chloride in the presence of bipyridine (Bpy).

[0072] In the RGP method of the present invention, in which particles with polymerizable groups react with monomers in the presence of an initiator, the polymerization of monomers in the reaction mixture inevitably leads to the formation of some "free" polymers not attached to the particles. These unattached polymers can be removed by repeatedly washing the particles with a solvent (typically a hydrocarbon) in which the unattached polymer is soluble, or (at least in the case of metal oxides or other dense particles) by centrifuging the treated particles from the reaction mixture (with or without the addition of solvent or diluent), redispersing the particles in fresh solvent, and repeating these steps until the proportion of unattached polymers has decreased to an acceptable level. (The decrease in the proportion of unattached polymers can be tracked by thermogravimetric analysis of the polymer sample). Empirically, it seems that the presence of a small proportion of unattached polymers, on the order of 1% by weight, does not appear to have any seriously detrimental effect on the electrophoretic properties of the treated particles; in fact, in some cases, depending on the chemistry of the unattached polymers and the suspension, it may not be necessary to separate the particles with the attached polymer stabilizer layer from the unattached polymers before using the particles for electrophoretic display.

[0073] It has been found that there is an optimal range for the amount of polymer stabilizer layer that should form on electrophoretic particles, and that excessive polymer formation on the particles may reduce their electrophoretic properties. This optimal range will vary with several factors, including the density and size of the coated particles, the nature of the suspending medium in which the particles are intended to be used, and the nature of the polymer formed on the particles. For any given particle, polymer, and suspending medium, the optimal range is best determined empirically. However, as a general guideline, it should be noted that the denser the particles, the lower the optimal proportion of polymer by weight of the particles, and the finer the particles are divided, the higher the optimal proportion of polymer. Generally, the particles should be coated with at least about 2% by weight of the particles, and ideally at least about 4% by weight. In most cases, the optimal proportion of polymer will range from about 4% by weight to about 15% by weight of the particles, typically from about 6% by weight to about 15% by weight, and most preferably from about 8% by weight to about 12% by weight.

[0074] To incorporate functional groups for charge generation in pigment particles, comonomers can be added to the polymerization reaction medium. The comonomers can directly charge the core-shell particles or interact with charge control agents in the display fluid to impart the desired charge polarity and charge density to the core-shell particles. Suitable comonomers may include vinylphenylaminoethylamino-propyltrimethoxysilane, methacryloxypropyltrimethoxysilane, acrylic acid, methacrylic acid, vinyl phosphoric acid, 2-acrylamide-2-methylpropanesulfonic acid, 2-(dimethylamino)ethyl methacrylate, N-[3-(dimethylamino)propyl]methacrylamide, etc. Suitable comonomers may also include fluorinated acrylates or methacrylates such as 2-perfluorobutyl ethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, or 2,2,3,3,4,4,4-heptafluorobutyl methacrylate. Alternatively, charged or charged groups may be incorporated into the polymer via a bifunctional stabilizer used to provide polymerizable or initiating functionality to the pigment.

[0075] Functional groups, such as acidic or basic groups, can be provided in a "blocked" form during polymerization and then deblocked after polymer formation. For example, since ATRP cannot be initiated in the presence of acid, if it is desired to provide acidic groups within the polymer, esters such as tert-butyl acrylate or isobornyl methacrylate can be used, and the residues of these monomers in the final polymer can be hydrolyzed to provide acrylic acid or methacrylic acid residues.

[0076] When it is desirable to generate charged or chargeable groups on pigment particles and to produce a polymer stabilizer layer separately attached to the particles, it may be very convenient to treat the particles (after metal oxide coating) with a mixture of two reagents, one of which has charged or chargeable groups (or groups that will ultimately be treated to generate the desired charged or chargeable groups), and the other of which has polymerizable or polymerization-initiating groups. Ideally, both reagents should have the same or substantially the same functional groups as those reacting on the particle surface, such that if the reaction conditions change slightly, the relative rate of reaction between the reagents and the particles will change in a similar manner, while the ratio between the number of charged or chargeable groups and the number of polymerizable or polymerization-initiating groups will remain substantially constant. It will be understood that this ratio can be changed and controlled by varying the relative molar amounts of the two (or more) reagents used in the mixture. Examples of reagents that provide a potential charge but not a polymerizable group or polymerization initiation group include 3-(trimethoxysilyl)propylamine, N-[3-(trimethoxysilyl)propyl]diethylenetriamine, N-[3-(trimethoxysilyl)propyl]ethylene, and 1-[3-(trimethoxysilyl)propyl]urea; all of these silane reagents are available from United Chemical Technologies, Inc., Bristol, Pa. 19007. As already mentioned, an example of a reagent that provides a polymerizable group but not a charged group or a charged group is 3-(trimethoxysilyl)propyl methacrylate.

[0077] The core-shell particles of this invention are useful in the field of electrophoresis. First, the shell of the particles allows for the modification and control of the surface properties and charge of organic pigment particles. Therefore, different types of electrophoretic particles in the medium can be surface-modified using different silane treatments, which may contribute to efficient separation and thus improved electro-optic properties. The metal oxide layer allows the silane layer to be covalently attached to the particle surface. Unlike inorganic pigments, which may contain functional groups such as hydroxyl groups that provide reactive anchors for attaching organic substances to their surfaces, most organic pigments do not contain functional groups that readily react with general reagents. Therefore, by depositing a layer of metal oxide on the surface of organic pigment particles, the subsequent silane layer is strongly attached to the particle surface, making it unlikely that it will desorb from the surface, thus improving the efficiency of the treatment. The same applies to surface treatments that include a polymer stabilizer layer. This layer contributes to the stability of the particle dispersion because it prevents particle aggregation. The steric effect caused by polymer attachment on the pigment particle surface prevents particle aggregation. The stronger the attachment, the more effective the stabilization, because less polymer desorption from the particle surface is observed under stronger attachment. Therefore, when polymers are covalently bonded to the particle surface, more effective particle stabilization and improved electro-optic properties are generally observed.

[0078] The method of forming the shell of core-shell particles also contributes to improved electro-optic properties. Generally, metal oxide layers are formed by the precipitation of metal oxides resulting from the reaction of a metal oxide precursor with a reagent in an organic solvent. The resulting metal oxide precipitates on the surface of the pigment particles, which are present in the solvent. Liquid-phase methods can lead to uneven coating of the metal oxide, meaning a larger amount of metal oxide is required for more complete surface coverage. In contrast, the method disclosed herein uses a fluidized bed reactor, a gaseous stream of the metal oxide precursor, and then a gaseous stream of the reagent, allowing for the formation of a thinner, more uniform metal oxide layer. This translates to better optical properties for the core-shell particles, as a thicker metal oxide layer can result in higher light reflection on the shell, which would prevent optimal light absorption and lower saturation colors from appearing on the organic pigment particles. The gaseous stream of the metal oxide precursor in an inert gas causes the metal oxide precursor to complex (or adsorb) onto the surface of the organic pigment particles. This method is unfavorable for the presence of a large excess of precursor on the organic pigment particles, resulting in a more uniform and thinner metal oxide layer.

[0079] According to one aspect of the invention, organic pigment particles comprising a metal oxide layer can be prepared using a fluidized bed reactor as described above. The organic pigment particles are inserted into a reactor in the form of a powder bed and contacted with a gaseous stream containing a metal oxide precursor and an inert gas to form a mixture of the organic pigment particles and the metal precursor. The metal oxide precursor can be complexed onto the surface of the organic pigment particles and then reacted with a reagent to provide a metal oxide coating on the surface of the organic pigment particles. This method can be carried out in a continuous or batch process.

[0080] The amount of polymer stabilizer layer on the core-shell particles can be controlled. Excessive polymer formation on the particles can reduce their electrophoretic properties. The optimal range varies with several factors, including the density and size of the organic pigment, the density and thickness of the metal oxide layer, the nonpolar fluid nature of the electrophoretic medium, and the material properties of the polymer stabilizer layer. It has been found that the denser the particles, the lower the optimal proportion of polymer stabilizer layer by weight of the core-shell particles. Conversely, the finer the organic pigment core, the higher the optimal proportion of polymer stabilizer layer. The polymer stabilizer layer can be 1 to 50% by weight, or 2 to 30% by weight, or 4 to 20% by weight, or 5 to 15% by weight of the core-shell particles.

[0081] The electrophoretic medium containing core-shell particles of the present invention can be used to form an electrophoretic device. This electrophoretic device can be an electrophoretic display containing an electro-optic material layer containing the electrophoretic medium, wherein the electrophoretic medium can be encapsulated in microcapsules or micropores. Figure 2The figure illustrates an example of such an electrophoresis apparatus 200. In this example, the electrophoresis apparatus includes an electro-optic material layer 225 containing an electrophoretic medium 220 encapsulated in a microcapsule 250. The electrophoresis apparatus also includes a first transparent electrode layer 210 and a second electrode layer 240. The second electrode layer 240 is attached to the electro-optic material layer via an adhesive layer 230. The electrophoresis apparatus may include a second adhesive layer ( Figure 2 (Not shown in the image), which is used to attach the first light-transmitting layer 210 to the electro-optic material layer 225. In addition to containing microcapsules 250, the electro-optic material layer 225 may also contain an adhesive 222. Figure 2 In this example, the electrophoretic medium 220 contains two types of particles in a nonpolar fluid. One or more of these particle types can be core-shell particles containing an organic pigment core and a shell containing a metal oxide layer and a silane layer. The particles can be moved by applying an electric field throughout the microcapsule 250.

[0082] The electrophoretic medium of this invention can be used to form electrophoretic assemblies such as front-plane laminates and dual-release sheets. Figure 3 As shown, in some embodiments, the front planar laminate 300 includes a light-transmitting electrode layer 310, an electro-optic material layer 325, and a release sheet 360. The release sheet 360 is attached to the electro-optic material layer 325 via an adhesive layer 330. In addition to containing microcapsules 350, the electro-optic material layer 325 may also contain an adhesive 322. Figure 3 In this example, the electrophoretic medium 320 contains two types of particles in a nonpolar fluid. One or more of these particle types can be a core-shell structure containing an organic pigment core and a shell containing a metal oxide layer and a silane layer. Removing the release sheet 360 and attaching a backplate containing an electrode layer to the exposed surface of the electro-optic material layer 325 via an adhesive layer 330 results in the formation of an electrophoretic apparatus.

[0083] In another implementation scheme, such as Figure 4 As shown, the dual release sheet 400 includes two adhesive layers (475 and 485) and two release sheets (470 and 480). Specifically, in this example, the first release sheet 470 is attached to the electro-optic material layer 425 using the first adhesive layer 475. The second release sheet 480 is attached to the electro-optic material layer 425 using the second adhesive layer 485. Figure 4 In one example, the electrophoretic medium 420 contains two types of particles in a nonpolar fluid. One or more of these particle types may be a core-shell structure containing an organic pigment core and a shell containing a metal oxide layer and a silane layer. Removing the release sheet 470 and attaching the first transparent electrode layer to the exposed surface of the electro-optic material layer 425 via the adhesive layer 475, and removing the release sheet 480 and attaching a backplate including a second electrode to the exposed surface of the other side of the electro-optic material layer 425, results in the formation of an electrophoretic apparatus.

[0084] In another embodiment, the electrophoretic medium of the present invention can be used to form an electro-optic assembly, wherein the electro-optic assembly is an inverted front-plane laminate. The inverted front-plane laminate sequentially includes (i) a first electrode layer, (ii) a first adhesive layer, (iii) an electro-optic material layer containing the encapsulated electrophoretic medium, and (iv) a release sheet. The inverted front-plane laminate may further include a second adhesive layer between the electro-optic material layers. The inverted front-plane laminate can be converted into an electro-optic device by removing the release sheet and attaching the second electrode layer to the exposed electro-optic material layer (or to the second adhesive layer).

[0085] The electrophoretic medium of the electrophoresis apparatus or assembly of the present invention comprises a plurality of at least one type of disclosed core-shell particles. The electrophoretic medium may further comprise a plurality of another type of core-shell particles or different types of charged electrophoretic particles. The electrophoretic medium may also comprise more than two types of core-shell particles or other types of charged electrophoretic particles. Different types of core-shell particles may have different colors.

[0086] The nonpolar fluid in which the electrophoretic particles are dispersed can be transparent and colorless. For high particle mobility, it preferably has a dielectric constant of about 2 to about 30, more preferably about 2 to about 15. Examples of suitable dielectric solvents include hydrocarbons such as isopar, decalin, 5-ethylidene-2-norbornene, fatty oils, paraffin oils, silicone fluids, aromatic hydrocarbons such as toluene, xylene, phenylxylene ethane, dodecylbenzene, or alkylnaphthalene, halogenated solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorotrifluorotoluene, 3,4,5-trichlorotrifluorotoluene, chloropentafluorobenzene, dichlorononane, or pentachlorobenzene, and perfluorinated solvents such as FC-43, FC-70, or FC-5060 from 3M, St. Paul MN, low molecular weight halogenated polymers such as poly(perfluoropropylene oxide), poly(chlorotrifluoroethylene), such as Halocarbon Oil from Halocarbon Products, River Edge, NJ, and perfluorinated polyalkyl ethers such as Galden from Ausimont or Krytox Oil and Greases from DuPont, Delaware. The K-Fluid series is a polydimethylsiloxane-based silicone oil (DC-200) from Dow-corning.

[0087] The content of electrophoretic particles in nonpolar fluids can vary. For example, one type of particle can account for 0.1% to 50% of the volume of the nonpolar fluid, preferably 0.5% to 15%. Example

[0088] Embodiments of the present invention are described below. The present invention is not limited to these embodiments.

[0089] Example 1

[0090] Pigment Red 122 particles with metal oxide layers 151.2 g of Pigment Red 122 powder (a quinacridone pigment supplied by Clairiant AG in Basel, Switzerland, under the name Ink Jet Magenta E 02) was loaded into a fluidized bed reactor, which was fed trimethylaluminum in a nitrogen stream, followed by a water / nitrogen stream. The resulting particles were dried to provide Pigment Red 122 particles with an alumina layer of approximately 1 nm thickness.

[0091] Example 2

[0092] Pigment Red 122 particles with metal oxide and silane layers Add (a) 10.0 g of Pigment Red 122 particles with a metal oxide layer from Example 1, (b) 40 g of ethanol, (c) 0.5 g of deionized water, and (d) 100 g of zirconia beads (1.7–2.4 mm) to a 100 mL plastic bottle. The mixture was placed on a roller mill and mixed for approximately 16 hours. The dispersion was then filtered through a 200-micron mesh into a round-bottom flask. This is Sample A.

[0093] Add 7.1 g of a 40% by weight solution of vinylbenzylaminoethylaminopropyltrimethoxysilane in methanol (Xiameter OFS-6032 silane supplied by Dow), 1.6 g of deionized water, and 0.6 g of glacial acetic acid to a separate 100 mL plastic bottle. Place the mixture on a roller mill for one hour. This is Sample B.

[0094] Sample B was then added to the flask containing sample A, and the pH of the mixture was adjusted to 9 using 0.1 M ammonium hydroxide solution. The resulting dispersion was stirred at room temperature with a high-mounted stirrer for 60 minutes, and 30 g of ethanol was added to the flask. The resulting mixture was centrifuged at 5000 rpm for 30 minutes. The supernatant was discarded, and the remaining material was dried overnight in a vacuum oven at 70°C. This is sample C.

[0095] Example 3.

[0096] Core-shell particles with metal oxide layers, silane layers, and polymer stabilizer layersAdd (a) 10 g of sample C particles from Example 2, (b) 72.5 g of toluene, and (c) 13.3 g of lauryl methacrylate (LMA) to a 250 mL plastic bottle. Mix the dispersion for 1 hour using an IKA Ultra Turrax mixer at 12,000 rpm. Then, transfer the dispersion to a round-bottom flask, purge with nitrogen, and heat to 65 °C. After heating at 65 °C for one hour, rapidly inject an initiator solution containing 0.2 g of 2,2′-azobis(2-methylpropionitrile) (AIBN) in 4.2 g of toluene into the flask and allow the reaction to proceed for 16 hours. Collect the resulting dispersion in a 1 L plastic bottle and centrifuge at 4500 rpm for 30 minutes. Discard the supernatant. Mix the remaining material with 200 mL of toluene and discard the supernatant. Wash with toluene, centrifuge again, and remove the supernatant. Then, collect the remaining material and dry it overnight in a vacuum oven at 70 °C. The obtained solid particles are sample D.

[0097] Example 4

[0098] Electrophoretic media In a 100 mL container, add (a) 8.65 g of particles from sample D, (b) 36.9 g of isoparaffin solvent (Isopar E, supplied by ExxonMobil), and (c) 2.47 g of 70 wt% CCA041 solution. The mixture is sonicated for 90 minutes and then mixed in a rolling mill for one hour. The sonication and mixing are repeated 10 times. The dispersion is then filtered through a 200 μm mesh.

[0099] Example 5

[0100] Pigment Red 122 particles with metal oxide and silane layers Add (a) 10.0 g of Pigment Red 122 particles with a metal oxide layer from Example 1, (b) 40 g of ethanol, (c) 0.5 g of deionized water, and (d) 100 g of zirconia beads (1.7–2.4 mm) to a 100 mL plastic bottle. The mixture was placed on a roller mill and mixed for approximately 16 hours. The dispersion was then filtered through a 200-micron mesh into a round-bottom flask. This is Sample E.

[0101] Add 4.7 g of methacryloxypropyltrimethoxysilane (Xiameter OFS-6030 silane supplied by Dow), 1.6 g of deionized water, and 0.6 g of glacial acetic acid to a separate 100 ml plastic bottle. Stir the mixture on a roller mill for one hour. This is sample F.

[0102] Sample F was then added to the flask containing sample E. The pH of the mixture was adjusted to 9 using 0.1 M ammonium hydroxide solution. The resulting dispersion was stirred at room temperature with a high-speed stirrer for 60 minutes, and 30 g of ethanol was added to the flask. The resulting mixture was centrifuged at 5000 rpm for 30 minutes. The supernatant was discarded, and the remaining material was dried overnight in a vacuum oven at 70 °C. This is sample G.

[0103] Example 6

[0104] Electrophoretic media In a 100 mL container, add (a) 8.65 g of particles from sample G, (b) 36.9 g of isoparaffin solvent (Isopar E, supplied by ExxonMobil), and (c) 2.47 g of 70 wt% CCA041 solution. The mixture is sonicated for 90 minutes and then mixed in a rolling mill for one hour. The sonication and mixing are repeated 10 times. The dispersion is then filtered through a 200 μm mesh.

[0105] Example 7.

[0106] A control sample of Pigment Red 122 (supplied by Clariant AG, Basel, Switzerland, as Ink JetMagenta E 02) was modified with vinyl benzyl chloride and lauryl methacrylate polymers as described in U.S. Patent Application No. 2014 / 0340430 (Example 1).

[0107] Thermogravimetric analysis Thermogravimetric analysis (TGA) was used to assess the adhesion of the silane-polymer. Within a temperature range of 115–365 °C, a relative mass loss of 13.6% was observed for sample D in Example 3, and a relative mass loss of 11.0% for sample G in Example 5. In contrast, within the same temperature range, a mass loss of only 3.6% was observed for the unmodified pigment red 122Ink Jet MagentaE 02. These results indicate that the silane and polymer were successfully bonded to the pigment surface.

[0108] Measurement of zeta potential The zeta potential values ​​of the pigment samples were measured by titration of the corresponding pigment dispersions in Isopar E using a standard solution of charge control agent in Isopar E and a Colloidal Dynamics ZetaProbe.

[0109] Figure 5 The graphs provide the zeta potential measurements of pigment particles from Example 3 (sample D), Example 5 (sample G), and Example 7 (control). Figure 5The data show that pigment 122, functionalized with alumina-vinylbenzylaminoethylaminopropyltrimethoxysilane-laurate methacrylate prepared in Example 3, has a zeta potential plateau of approximately 105 mV. Pigment 122, functionalized with alumina-methacryloyloxypropyltrimethoxysilane-laurate methacrylate prepared in Example 6, has a zeta potential plateau of approximately 8 mV. This indicates that for pigments containing a metal oxide layer, the zeta potential can be adjusted over a wide range as the functionalized material is changed. In contrast, pigment red 122, functionalized with vinylbenzylchloro-laurate methacrylate (without a metal oxide layer), has a zeta potential plateau at approximately 50 mV.

[0110] While preferred embodiments of the invention have been shown and described herein, it should be understood that these embodiments are provided by way of example only. Many variations, modifications, and substitutions will appear to those skilled in the art without departing from the spirit of the invention. Therefore, the appended claims are intended to cover all such variations that fall within the spirit and scope of the invention.

[0111] All contents of the aforementioned patents and applications are incorporated herein by reference in their entirety.

Claims

1. A method for manufacturing an electrophoretic medium, the electrophoretic medium comprising a plurality of first-type core-shell particles and a nonpolar fluid, wherein each of the plurality of first-type core-shell particles comprises: A core containing organic pigments; A shell comprising a metal oxide layer and a silane layer; in, The method includes the following steps: The metal oxide layer is formed on the surface of the organic pigment using a fluidized bed reactor, which is achieved by: Organic pigments are inserted into a fluidized bed reactor in the form of a powder bed. The powder bed is brought into contact with a gaseous stream containing inert gases and metal oxide precursors. The powder bed is brought into contact with a gaseous stream containing an inert gas and a reagent containing a metal oxide precursor to react and form the metal oxide; and The silane layer is formed from a silane compound containing a first functional group, wherein the first functional group reacts with a metal oxide.

2. The manufacturing method according to claim 1, wherein the silane compound further comprises a second functional group, wherein the second functional group is selected from alkyl groups, haloalkyl groups, alkenyl groups, aryl groups, hydroxyl groups, carboxyl groups, sulfate ester groups, sulfonate ester groups, phosphate ester groups, phosphonic acid groups, amine groups, quaternary ammonium groups, dimethylsiloxane groups, ester groups, amide groups, and ethyleneimine groups.

3. The manufacturing method according to claim 1, wherein the shell further comprises a polymer stabilizer layer, wherein the polymer stabilizer layer is formed by the reaction of a silane layer and a monomer or macromonomer, wherein the silane compound comprises a third functional group, wherein the monomer or macromonomer comprises a fourth functional group, and wherein the third functional group of the silane compound reacts with the fourth functional group of the monomer or macromonomer.

4. The manufacturing method according to claim 1, wherein the metal oxide layer comprises aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, zinc oxide, or a mixture thereof.

5. The manufacturing method according to claim 1, wherein the first functional group is selected from alkoxy, alkylamino, halide, hydrogen and hydroxyl.

6. The manufacturing method according to claim 1, wherein the metal oxide precursor is selected from trimethylaluminum, triethylaluminum, dimethylaluminum chloride, diethylaluminum chloride, trimethoxyaluminum, triethoxyaluminum, dimethylaluminum propionate oxide, triisopropylaluminum oxide, tributoxyaluminum, tri(dimethylamino)aluminum, tri(diethylamino)aluminum, tri(propylamino)aluminum, aluminum trichloride, trichlorosilane, hexachlorodisilane, silicon tetrachloride, tetramethoxysilane, tetraethoxysilane, tri(tert-pentoxy)silane, etc. Silanols, tetraisocyanate silanes, silicon tetrachloride, tris(methylamino)silane, tris(ethylamino)silane, titanium tetrachloride, titanium tetraiodide, tetramethoxytitanium, tetraethoxytitanium, isopropyl titanium oxide, tetra(methylamino)titanium, tetra(ethylamino)titanium, dimethyl zinc, diethyl zinc, isopropyl methyl zinc oxide, zirconium tetrachloride, zirconium tetraiodide, tetramethoxyzirconium, tetraethoxyzirconium, tetraisopropoxyzirconium, tetrabutoxyzirconium, tetra(methylamino)zirconium, tetra(ethylamino)zirconium and mixtures thereof.

7. The manufacturing method according to claim 1, wherein the reagent is selected from water, oxygen, ozone, and mixtures thereof.

8. The manufacturing method according to claim 1, wherein the thickness of the metal oxide layer is 0.5 nm to 2 nm.

9. The manufacturing method according to claim 3, wherein the third functional group of the silane compound is selected from epoxy, vinyl, styrene, acryloyl, methacryloyl, methacryloyloxyalkyl, amino, hydroxy, carboxyl, alkoxy and chloride.

10. The manufacturing method according to claim 3, wherein the fourth functional group of the monomer or macromonomer is selected from vinyl, styrene, acryloyl, methacryl, methacryloyloxyalkyl, epoxy, amino, hydroxyl, carboxyl and chloride.

11. The manufacturing method according to claim 1, wherein the organic pigment is selected from azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, isoindoline pigments, anthrone pigments, indanone pigments, carbon black pigments, rhodamine pigments, aniline pigments, carbon black pigments, and mixtures thereof.

12. The manufacturing method according to claim 1, wherein the organic pigment is selected from CI Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 60 and 79; Pigment Red 2, 4, 5, 9, 12, 14, 38, 48:2, 48:3, 48:4, 52:2, 53:1, 57:1, 81, 112, 122, 144, 146, 147, 149, 168, 170, 176, 177, 179, 184, 185, 187, 188, 208, 209, 210, 214, 242, 254, 255, 257, 262, 264, 282 and 285; CI Pigments Violet 1, 19, 23 and 32; CI Pigments Yellow 1, 3, 12, 13, 14, 15, 16, 17, 73, 74, 81, 83, 97, 109, 110, 111, 120, 126, 127, 137, 138, 139, 150, 151, 154, 155, 174, 175, 176, 180, 181, 184, 191, 194, 213 and 214; CI Pigments Green 7 and 36; CI Pigments Black 1 and 7; CI Pigments Brown 25, 32, 41; Pigments Orange 5, 13, 34, 36, 38, 43, 61, 62, 64, 68, 67, 72, 73 and 74, and mixtures thereof.

13. A method for manufacturing an electrophoretic medium comprising multiple core-shell particles and a nonpolar fluid, comprising the following steps: Provides organic pigment particles; Organic pigment particles are introduced into a fluidized bed reactor in the form of a powder bed; The powder bed is brought into contact with a gaseous stream containing inert gases and metal oxide precursors; A powder bed is brought into contact with a gas stream containing a reagent to form organic pigment particles having a metal oxide layer on its surface, wherein the reagent is selected from water, oxygen, ozone and mixtures thereof. Organic pigment particles having a metal oxide layer are reacted with a silane compound in an organic solvent to form a silane layer, wherein the silane compound comprises a first functional group and a third functional group, wherein the first functional group reacts with a metal oxide to form organic pigment particles comprising a metal oxide layer and a silane layer. The plurality of core-shell particles are combined with the nonpolar fluid.

14. The method for manufacturing an electrophoretic medium according to claim 13, further comprising, prior to the step of combining the plurality of core-shell particles and a nonpolar fluid, reacting organic pigment particles having a metal oxide layer and a silane layer with a monomer or macromonomer containing a fourth functional group to form a plurality of core-shell particles, wherein a third functional group of the silane reacts with a fourth functional group of the monomer or macromonomer.

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