JP2021515272A - Composite particles and their manufacturing methods - Google Patents

Abstract

There is provided a composite particle comprising a base particle and a plurality of hydrophilic oligomeric groups extending from the outer portion of the base particle, wherein the base particle comprises a crosslinked polyurea and at least one of a pigment and a dye. The crosslinked polyurea may form a network structure throughout the base particles. The method for producing composite particles is to provide either a dye-containing solution or a pigment-containing dispersion in a water-dispersible polyfunctional isocyanate dissolved in a water-mixable solvent, and to form an aqueous emulsion of the solution / dispersion. This involves stirring the emulsion while the polyfunctional isocyanate is converted to the crosslinked polyurea, and separating the composite particles containing the crosslinked polyurea with the dye / pigment from the emulsion.

Description

Field of Invention The present invention relates to composite particles used in an electrophoretic display medium and an improved method for producing the composite particles.

Background of the Invention In the present specification, the term "electro-optic" applied to a material or display is the conventional meaning in the art of image formation, wherein at least one optical property is different. It is used to refer to a material having the first and second display states, which changes from the first display state to the second display state by applying an electric field to the material. Optical properties are typically colors that are perceptible to the human eye, but are visible in the case of displays intended for other optical properties, such as light transmission, reflection, luminescence, or machine reading. It can be a pseudo-color in the sense of a change in reflection of electromagnetic wave length outside the range.

Some electro-optical materials are solid in the sense that the material has a solid outer surface, but may and often have an internal liquid or gas filled space. Such a display using a solid-state electron-optical material may be hereinafter referred to as a "solid-state electron-optical display" for convenience. Thus, a "solid-state electro-optical display" includes a rotating bicolor member display, an encapsulated electrophoresis display, a microcell electrophoresis display, and an encapsulated liquid crystal display.

As used herein, the terms "bistable" and "bisstability" differ in at least one optical property, such as black and white, in their conventional sense in the art. A display that includes display elements with first and second display states in which any given element is driven using address pulses of finite duration to display either the first or second display. Refers to a display in which, after exhibiting a state, after the address pulse has stopped, the state lasts at least several times, for example, at least four times the shortest duration of the address pulse required to change the state of the display element. Used for. Some particle-based electrophoretic displays are stable not only in the black and white states of their polarities, but also in multicolor displays with three or more states, such as three or more colors. .. For convenience, the term "bisstability" can be used herein to include display devices with two or more display states.

One type of electro-optical display that has been the subject of intense research and development over the years is a particle-based electrophoretic display in which multiple charged particles move through a fluid under the influence of an electric field. Electrophoretic displays can have the attributes of good brightness and contrast, wide viewing angle, state bistability, and low power consumption when compared to liquid crystal displays. Nevertheless, long-term image quality issues with these displays have hampered their widespread use. For example, the particles that make up an electrophoretic display tend to settle, resulting in an inadequate useful life for these displays.

Numerous patents and applications have been transferred to or in the name of Massachusetts Institute of Technology (MIT), E Ink Corporation, E Ink California, LLC, and affiliates, including encapsulation and microcell electrophoresis and Various techniques used in other electro-optical media are described. The encapsulated electrophoresis medium contains a large number of small capsules, each of which itself contains an internal phase containing particles that can be moved by electrophoresis in the fluid medium and a capsule wall surrounding the internal phase. Typically, the capsule is itself retained in a polymer binder to form a coherent layer positioned between the two electrodes. In microcell electrophoresis displays, charged particles and fluids are not encapsulated within microcapsules, but instead are retained within a plurality of cavities formed in a carrier medium, which is typically a polymeric film. The techniques described in these patents and applications include:
(A) Electrophoretic particles, fluids, and fluid additives; eg, US Pat. Nos. 5,961,804; 6,017,584; 6,120,588; 6,120,839; 6,262,706; 6,262,833; 6,300,932; 6,323,989; 6,377,387; 6,515,649; 6,6 538,801; 6,580,545; 6,652,075; 6,693,620; 6,721,083; 6,727,881; 6,822 782; 6,831,771; 6,870,661; 6,927,892; 6,956,690; 6,958,849; 7,002,728 No. 7,038,655; No. 7,052,766; No. 7,110,162; No. 7,113,323; No. 7,141,688; No. 7,142,351; No. No. 7,170,670; No. 7,180,649; No. 7,226,550; No. 7,230,750; No. 7,230,751; No. 7,236,290; No. 7, 247,379; 7,277,218; 7,286,279; 7,312,916; 7,375,875; 7,382,514; 7,390, 901; 7,411,720; 7,473,782; 7,532,388; 7,532,389; 7,572,394; 7,576,904 No. 7,580,180; No. 7,679,814; No. 7,746,544; No. 7,767,112; No. 7,848,006; No. 7,903,319; 7,951,938; 8,018,640; 8,115,729; 8,119,802; 8,199,395; 8,257,614; 8,8, 270,064; 8,305,341; 8,361,620; 8,363,306; 8,390,918; 8,582,196; 8,593 718; 8,654,436; 8,902,491; 8,961,831; 9,052,564; 9,114,663; 9,158,174 9,341,915; 9,348,193; 9,361,836; 9,366,935; 9,372,380; 9,382,427; and No. 9,423,666; and US Pat. Publication No. 2003/0048522; No. 2003/0151029; No. 2003/016480; No. 2003/016927; No. 2003/0197916; No. 2004/0030125; No. 2005/0012980; No. 2005/01363347 No. 2006/0132896; No. 2006/0281924; No. 2007/0268567; No. 2009/0009852; No. 2009/02526499; No. 2009/0225398; No. 2010/0148385; No. 2011/0217639; No. 2012/0049125; 2012/0112131; 2013/0161565; 2013/0193385; 2013/0244149; 2014/0011913; 2014/0078024; 2014/0078573; 2014/ No. 0078576; No. 2014/0078857; No. 2014/010467; No. 2014/0231728; No. 2014/0339481; No. 2014/0347718; No. 2015/0015932; No. 2015/0177589; No. 2015/0177590 See 2015/018559; 2015/0218384; 2015/0241754; 2015/0248045; 2015/0371425; 2015/0378236; 2016/0139483; and 2016/0170106. ;
(B) Capsules, binders, and encapsulation processes; see, eg, US Pat. Nos. 6,922,276 and 7,411,719;
(C) Microcell structure, wall material, and method of forming microcells; see, eg, US Pat. Nos. 7,072,095 and 9,279,906;
(D) Methods for filling and sealing microcells; see, for example, U.S. Pat. Nos. 7,144,942 and 7,715,088;
(E) Coatings and subassemblies containing electro-optic materials; see, eg, US Pat. Nos. 6,982,178 and 7,839,564;
(F) Backplanes, adhesive layers, and other auxiliary layers, and methods used in displays; see, eg, US Pat. Nos. 7,116,318 and 7,535,624;
(G) Color formation and color adjustment; see, for example, U.S. Pat. Nos. 7,075,502 and 7,839,564;
(H) How to drive a display; see, for example, U.S. Pat. Nos. 7,012,600 and 7,453,445;
(I) Application of displays; see, for example, U.S. Pat. Nos. 7,312,784 and 8,009,348; and (j) U.S. Pat. Nos. 6,241,921 and U.S. Patent Application Publication No. 2015/0277160. Non-electrophoretic displays described in; and application of non-display encapsulation and microcell techniques; see, eg, US Patent Application Publication Nos. 2015/0005720 and 2016/0012710.

Many of the aforementioned patents and applications can replace the walls surrounding individual microcapsules in an encapsulated electrophoresis medium with a continuous phase, thus producing a so-called polymer-dispersed electrophoresis display, in which the electricity The running medium comprises multiple separate droplets of the electrophoresis fluid and a continuous phase of the polymeric material, and the individual droplets of the electrophoresis fluid in such a polymeric dispersion electrophoresis display are separate capsule membranes. We recognize that even if is not associated with each individual droplet, it can be considered a capsule or microcapsule; see, for example, US Pat. No. 6,866,760 above. Therefore, for the purposes of this application, such polymer-dispersed electrophoresis media are considered subspecies of encapsulated electrophoresis media.

An electrophoretic display typically includes a layer of electrophoretic material and at least two other layers located on either side of the electrophoretic material, one of which is the electrode layer. In most such displays, both layers are electrode layers, and one or both of the electrode layers are patterned to define the pixels of the display. For example, one electrode layer may be patterned on an elongated row electrode, the other electrode layer may be patterned on an elongated column electrode running perpendicular to the row electrode, and the pixel is the intersection of the row electrode and the column electrode. It is defined by a line. Alternatively, more generally, one electrode layer has the form of a single continuous electrode, the other electrode layer is patterned into a matrix of pixel electrodes, each defining one pixel of the display. In another type of electrophoresis display, which is intended to be used with a stylus, printhead, or similar moving electrode separate from the display, only one of the layers adjacent to the electrophoresis layer contains the electrodes. The layer opposite the electrophoresis layer is typically a protective layer intended to prevent the movable electrode from damaging the electrophoresis layer.

Encapsulated electrophoresis displays typically do not go into the clustering and poor settling mode of traditional electrophoresis devices, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (The use of the word "printing" is: premeter coating, eg patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating, eg knife overroll. Coating, forward and reverse roll coating; gravure coating; immersion coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating, silk screen printing process; electrostatic printing process; thermal printing process; inkjet printing process; electrophoresis Deposition (see US Pat. No. 7,339,715); and is intended to include all forms of printing and coating, including but not limited to other similar techniques). Therefore, the resulting display can be flexible. Moreover, since the display medium can be printed (using various methods), the display itself can be inexpensively manufactured.
In the design of electrophoretic displays, it is often necessary to adjust the properties of electrodynamically moving pigment particles to meet a number of criteria, and the requirements of one criterion violate the requirements of another. Is not uncommon. For example, it may be required to provide an optically transparent color pigment that is easily switched by a dielectrophoresis mechanism. In order for such pigments to be transparent, they must contain particles small enough not to scatter visible light. However, in order to allow dielectrophoretic switching, the particles should ideally be large, so the electric field gradient can elicit significant dipole moments. One way to meet both requirements is to construct composite particles in which small pigment particles (which require transparency) are incorporated into large superpartners (demonstrating proper dielectrophoretic mobility). Therefore, there is a need for an efficient method of incorporating small pigment particles into a large complex that can properly function itself with respect to electrokinetic mobility.

U.S. Pat. No. 5,961,804 U.S. Pat. No. 6,017,584 U.S. Pat. No. 6,120,588 U.S. Pat. No. 6,120,839 U.S. Pat. No. 6,262,706

Abstract of the Invention According to one aspect of the present invention, it is a composite particle containing a base particle and a plurality of hydrophilic oligomer groups on the outer portion of the base particle, and the base particle is a crosslinked polyurea and a pigment and a dye. Composite particles are provided that include at least one of the following. The crosslinked polyurea may form a network throughout the base particles.

According to another aspect of the present invention, a method for producing composite particles is provided. The method is to provide either a dye-containing solution or a pigment-containing dispersion in an aqueous dispersible polyfunctional isocyanate dissolved in a water-miscible solvent, to form an aqueous emulsion of the solution / dispersion, the polyfunctionality. It involves stirring the emulsion while the sex isocyanate is converted to crosslinked polyurea and separating the composite particles containing the crosslinked polyurea with the dye / pigment from the emulsion.

Yet another aspect of the invention is an electrophoresis medium comprising a plurality of charged particles that are placed in the fluid and capable of moving in the fluid under the influence of an electric field, wherein at least one of the particles is present. It is to provide an electrophoretic medium produced by the method according to an embodiment of the invention. The charged particles and fluids may be confined within multiple capsules or microcells. Alternatively, the charged particles and fluid may be present as a plurality of separate droplets surrounded by a continuous phase containing the polymeric material. The fluid may be liquid or vapor. An electrophoretic material containing an electrophoretic medium may be incorporated into an electrophoretic display that includes a layer of electrophoretic material and at least one electrode arranged to apply an electric field to the layer of electrophoretic material.

A display incorporating an electrophoresis medium produced according to various embodiments of the present invention can be used in any application in which a prior art electro-optical display has been used. Thus, for example, the displays of the invention can be used in e-book readers, portable computers, tablet computers, mobile phones, smart cards, signs, watches, shelf labels, variable transmission windows, and flash drives.

These and other aspects of the invention will become apparent in light of the following description.

The drawings show one or more realizations of the concept of the invention, not as a limitation, but merely as an example. In the figure, similar reference numerals refer to the same or similar elements.

FIG. 1 is a schematic view of the prior art method of forming microcapsules.

FIG. 2 is a schematic view of a method for forming composite particles according to an embodiment of the present invention.

Detailed Description The following detailed description provides a number of specific details as examples to provide a complete understanding of the relevant teachings. However, it will be apparent to those skilled in the art that the teachings of the present invention can be practiced without such details.

Composite particles according to various embodiments of the present invention include crosslinked polyureas that form a network structure throughout the base particles. As used herein and in the claims, forming a "network over the entire base particle" means that the crosslinked polyurea is present at multiple locations / radii within the total thickness of the base particle. Means. Therefore, the polyurea shell of microcapsules is considered to deviate from the definition of "reticulated structure over the entire base particle" because the shell generally exists only along the outer circumference of the microcapsules, for example.

In one method according to an embodiment of the invention, the crosslinked polyurea may be obtained from a water-dispersible polyfunctional isocyanate. Upon contact with water, the isocyanate groups of the polyfunctional isocyanate are hydrolyzed, releasing carbon dioxide and forming amines. Amino groups react with isocyanates faster than water; therefore newly formed amines tend to react with adjacent non-hydrolyzed isocyanates. This reaction produces urea groups, so the end result of the reaction is cross-linked polyurea, which also contains some free amino groups.

Water-dispersible polyfunctional isocyanates typically contain hydrophilic oligomeric groups (often aliphatic oligomers such as poly (ethylene oxide)), and multiple isocyanate groups. The portion of the molecule that retains the isocyanate group is essentially water insoluble. When the polyfunctional isocyanate is combined with an immiscible solvent and emulsified in a continuous aqueous phase, the mixture of the polyfunctional isocyanate and the solvent forms micelles as shown in FIG. The poly (ethylene oxide) unit (11) is solvated with water to stabilize the water interface while the higher hydrophobic interior of the micelle contains most of the isocyanate functional group (10). The isocyanate group (10) may react as described above to form a polyurea shell (13) around an immiscible solvent (12) to form microcapsules.

Although not bound by theory, it is thought that by first dissolving the water-dispersible polyfunctional isocyanate in a water-miscible solvent, composite particles having a polyurea network structure over the entire base particles of the composite can be formed. Be done. With reference to FIG. 2, which is a schematic diagram of an embodiment of the present invention, a mixture of water-dispersible polyfunctional isocyanate and a water-miscible solvent is introduced into water (with stirring) and thus hydrophilic oligomeric groups (11). ) To form droplets (14) of solvent stabilized at the aqueous interface. Diffusion of water into the droplet (14) of the solvent polymerizes the polyfunctional isocyanate by the hydrolysis reaction and amine condensation described above, while diffusion of the solvent (14) from the droplet to the aqueous phase is droplet. Shrink. At equilibrium, the droplets contain very little solvent, resulting in polyurea (15) that is almost crosslinked over the entire thickness of the base particles, and any other initially dissolved or dispersed in the solvent. Base particles are obtained, including the material. For example, by introducing a soluble dye or insoluble pigment into a solution of a water-miscible solvent and a water-dispersible polyfunctional isocyanate, the dye or pigment is captured within the polyurea network formed after polymerization in the aqueous phase. A composite particle having a base particle is obtained.

Therefore, various methods for producing composite particles according to the present invention first dissolve the dye and the water-dispersible polyfunctional isocyanate in a water-miscible solvent, or the pigment, the water-dispersible polyfunctional isocyanate. And disperse in a solution of a water-miscible solvent. The weight ratio of the water-dispersible polyfunctional isocyanate to the water-miscible solvent is preferably 1: 3 to 3: 1 and most preferably 1: 2 to 2: 1. The amount of dye or pigment may depend on the desired opacity or transparency of the final composite particle.

In the second step, a mixture of dye / pigment, polyfunctional isocyanate, and water-miscible solvent is added to the aqueous phase. If desired, a surfactant may be added to the aqueous phase and / or the stirring speed may be varied to control, for example, the final particle size.

As mentioned above, as the water diffuses into the aqueous phase, the polyfunctional isocyanate is crosslinked via the hydrolysis reactions and amine condensations already described. The degree of cross-linking will depend on the temperature and time at which the reaction takes place. Increasing the length of time that the stained solution / pigment dispersion droplets are exposed to the aqueous phase will increase the degree of cross-linking.

Once the desired degree of cross-linking is reached, the resulting composite particles containing the cross-linked polyurea network and dye / pigment may be separated from the aqueous phase (containing the dissolved solvent). This can be achieved using any separation method known to those of skill in the art, including but not limited to filtration, centrifugation, drying, and combinations thereof. As described in more detail below, it is preferred that most, if not all, of the water be removed from the complex for further processing. Preferably, the particles may be separated from the aqueous phase by centrifugation and then dried to remove residual water and solvent.

Water-dispersible polyfunctional isocyanates that can be used to form composite particles according to various embodiments of the present invention, such as those sold under the trade name Bayhydur manufactured by Bayer Corporation, are skilled in the art. Is known to. The water-dispersible polyfunctional isocyanate preferably has an NCO content of about 5 to 35%, more preferably about 15 to 25%.

The water-miscible solvent that can be used in the methods for forming composite particles according to various embodiments of the present invention is preferably an organic solvent in which a water-dispersible polyfunctional isocyanate is soluble. Such solvents are known in the art and include, but are not limited to, tetrahydrofuran (THF), ketones, and esters. The solvent should not contain nucleophilic groups that can react with isocyanates. One particularly preferred water-miscible solvent is methyl acetate. The preferred solubility of the water-miscible solvent is at least 5%, more preferably at least 25% by weight. Dyes and pigments that can be used in composite particles according to various embodiments of the invention are also known to those of skill in the art. The dye is preferably soluble in one or both of the water-dispersible polyfunctional isocyanate and the water-miscible solvent. Dyes and pigments are also preferably insoluble in water and insoluble in the non-polar solvent of the electrophoretic medium to which the composite particles will be added. The soluble dyes that may be incorporated into the composite particles according to the present invention include, but are not limited to, Solvent Blue 70, Solvent Blue 67, Solvent Blue 136, Solvent Red 127, Solvent Red 130, Solvent Red 233, Solvent. Red 125, Solvent Red 122, Solvent Yellow 88, Solvent Yellow 146, Solvent Yellow 25, Solvent Yellow 89, Solvent Orange 11, Solvent Orange 99, Solvent Brown 29 is included.

Pigments that are insoluble in water-miscible solvents and water-dispersible polyfunctional isocyanates may be used in place of the method to prepare the composite particles of the invention. The pigment may be combined with a polyfunctional isocyanate / solvent solution to form a pigment dispersion, which is subsequently introduced into the aqueous phase. Pigments that may be incorporated into the composite particles according to the present invention include, but are not limited to, inorganic pigments, neat pigments, lake pigments, and organic pigments.

Examples of inorganic pigments include, but are not limited to, TiO ₂ , ZrO ₂ , ZnO, Al ₂ O ₃ , CI pigment black 26 or 28, or similar (eg, manganese ferrite black spinel or copper chromite). Black spinel) is included. Particles such as titania particles may be coated with a metal oxide such as aluminum oxide or silicon oxide.

Useful neat pigments include, but are not limited to, PbCrO ₄ , Cyan Blue GT 55-3295 (American Cyanamide Company, Wayne, NJ), Cibacron Black BG (Ciba Company, Inc., New). Del.), Cibacron Turquoise Blue G (Ciba), Cibalon Black BGL (Ciba), Orasol Black BRG (Ciba), Orasol Black BRG (Ciba), Orasol Black RBL (Ciba), Acetain , Wilmington, Del., Hereinafter abbreviated as "du Pont"), Cyan Scarlet N Ex (du Pont) (27290), Fiber Black VF (du Pont) (3023S), Luxol Fast Black (Solv. Black 17), Nirocine Base No. 424 (du Pont) (50415 B), Oil Black BG (du Pont) (Solv. Black 16), Rotalin Black RM (du Pont), Seven Brilliant Red 3 B (du Pont) ), Hectorene Black (Dye Specialties, Inc.), Azosol Brilliant Blue B (GAF, Dyestuff and Chemical Division, Wayne, N.J.) (Solv.Brilliant Blue9) 2), Azosol Fast Brilliant Red B (GAF), Azosol Fast Orange RA Conc. (GAF) (Solv. Orange 20), Azosol Fast Yellow GRA Conc. (GAF) (13900 A), Basic Black KMPA (GAF), Benzofix Black CW-CF (GAF) (35435), Cellitazol BNFV Ex Soluble CF (GAF) (Disp. ) (Disp. Blue 9), Type Black IA (GAF) (Basic Black 3), Diamine Black CAP Ex Conc (GAF) (30235), Diamond Black EAN Hi Con. CF (GAF) (15710), Diamond Black PBBA Ex (GAF) (16505); Direct Deep Black EA Ex CF (GAF) (30235), Hansa Yellow G (GAF) (11680); Indanthrone. (GAF) (59850), Indocarbon CLGS Conc. CF (GAF) (53295), Katien Deep Black NND Hi Conc. CF (GAF) (15711), Rapidogen Black 3 G (GAF) (Azoic Black 4); Sulfone Cyanine Black BA-CF (GAF) (26370), Zambezi Black VD ExConc. (GAF) (30015); Rubanox Red CP-1495 (The Shernin-Williams Company, Cleveland, Ohio) (15630); Raven 11 (Columbian Carbon Company, Atlanta, Ga. Aggregates), Statex B-12 (Columbian Carbon Co.) (Furness Black with an average particle size of 33 μm), and Chrome Green.

Lake pigments are particles that have or are colored with a dye that is precipitated on the surface of the particles. Lakes are metal salts of easily soluble anionic dyes. These are dyes of azo, triphenylmethane, or anthraquinone structure that contain one or more groups of sulfones or carboxylic acids. They are usually precipitated on the substrate with calcium, barium, or aluminum salts. Typical examples are Peacock Blue Lake (Cl Pigment Blue 24) and Persian Orange (Cl Acid Orange 7 Lake), Black M Toner (GAF) (mixture of carbon black and black dye precipitated on the lake). Is.

The organic pigment particles are not limited to these, but the CI pigments PR 254, PR122, PR149, PG36, PG58, PG7, PB28, PB15: 1, PB15: 2, PB15: 3, PB1: 4, PY83, PY138, PY150, PY155, or PY20, as well as the Color Index Handbook "New Pigment Application Technology" (CMC Publishing Co, Ltd, 1986) and "Printing Ink Technology" (CMC) Organic pigments used in the art can be included. Specific examples include Clarian Hostaperm Red D3G 70-EDS, Hostaperm Pink E-EDS, PV Fastred D3G, Hostaperm Red D3G 70, Hostaperm Blue B2G-EDS, HostaperM. Hostaparm Green GNX, BASF Irgazine Red L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; Sun Chemical Phthalocyanine Blue, Phthalocyanine Green, Theary Lido Yellow or Theary Lido A.

The colors presented by the dyes / pigments of the composite particles according to the present invention may be, for example, white, black, red, green, blue, cyan, magenta, or yellow. In addition to those colors, the particles reflect electromagnetic wave lengths outside the visible range in the case of display media intended for other distinct optical properties, such as light transmission, reflectance, luminescence, or machine reading. It may have a pseudo color in the sense of a change in rate.

It should also be noted that the composite particles may have various particle sizes. Useful sizes may range from 1 nm to about 100 μm. For example, smaller particles may have a size ranging from about 50 nm to about 800 nm. The larger particles may have a size of about 2 to about 50 times, more preferably about 2 to about 10 times the size of the smaller particles.

Composite particles produced according to various embodiments of the present invention may be further treated for surface modification. Such surface modification processes are known to those of skill in the art, such as those disclosed in US Patent Application No. 2015/0218384, the contents of which are incorporated herein by reference.

For example, the stability of the electrophoresis medium may be improved by either chemical bonding or cross-linking of the three-dimensionally stabilized polymer around the outside of the composite particles. The polymer stabilizer has a long polymer chain that can determine the particle size and colloidal stability of the system and preferably stabilize the composite particles in a hydrocarbon solvent. The sterically stabilized polymer is preferably about 1 to about 15 weight percent of the composite particles.

These polymer-coated composite particles (a) react with a reagent having a functional group capable of reacting with and binding to the particles and also having a polymerizable or polymerization initiating group, thereby causing a functional group. To react with the surface of the particle and attach a polymerizable group to it; and (b) conditions effective for inducing a reaction between the polymerizable or polymerization initiating group on the particle and at least one monomer or oligomer. Below, it may be prepared by a method comprising reacting the product of step (a) with at least one monomer or oligomer, thereby causing the formation of a polymer bound to the particles.

Since composite particles produced by various embodiments of the present invention are likely to have an amine group available on the surface of the particle, the available amine group is at least one capable of reacting with the amine. It may be present with the reagent of step (a) above having a functional group and at least one polymerizable group. For example, the reagents used in step (a) of this method (so-called "surface functionalization" step) may include isocyanate groups and acrylate groups, such as isocyanate ethyl acrylates. Alternatively, steps (a) and (b) use reagents that are already in polymer form if the sterically stabilized polymer contains functional groups such as isocyanate groups that can react with amine groups on the surface of the composite particles. It may be replaced by a single step.

As mentioned above, when reagents such as isocyanate ethyl acrylate are used in step (a), the polymer stabilizer will be one or more monomers or macros using various polymerization techniques known to those of skill in the art. It may be derived from the monomer. For example, polymer stabilizers are random graft polymerization (RGP), ionic random graft polymerization (IRGP), as described in US Pat. No. 6,822,782, the entire contents of which are incorporated herein by reference. ), And may be obtained by atom transfer radical polymerization (ATRP). As used herein and throughout the claims, "macromonomer" means a macromolecule with one end group that can act as a monomer.

Suitable monomers for forming polymer stabilizers include, but are not limited to, styrene, alphamethylstyrene, methylacrylic acid, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, T-butyl acrylate, t-butyl methacrylate, vinylpyridine, N-vinylpyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, lauryl acrylate, lauryl methacrylate, acrylic acid 2-Ethylhexyl, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate, n-octadecyl acrylate, n-octadecyl methacrylate, 2-perfluorobutyl ethyl acrylate , 2,2,2-Trifluoroethyl Methacrylic Acid, 2,2,3,3-Tetrafluoropropyl Methacrylic Acid, 1,1,1,3,3,3-Hexafluoroisopropyl Methacrylic Acid, 1,1 Methacrylic Acid , 1,3,3,3-hexafluoroisopropyl, acrylate 2,2,3,3,3-pentafluoropropyl, acrylate 2,2,3,3-tetrafluoropropyl, methacrylic acid 2,2,3 , 4,4,4-Hexafluorobutyl, and 2,2,3,3,4,5,4-heptafluorobutyl methacrylate, or the like. The macromonomer may contain a terminal functional group selected from the group consisting of an acrylate group, a vinyl group, or a combination thereof.

When describing the reagents used to provide the desired polymerizable or initiating functional groups, it does not rule out the possibility that the polymer stabilizer may be "bifunctional". For example, polymerization initiators with more than one ionic site (such as 4,4'-azobis (4-cyanovaleric acid)) are known and such initiators are used in the methods of the invention. May be good. Also, as mentioned above, the bifunctional compound has the form of a macromonomer-containing repeating unit capable of binding to the particle surface and other repeating units having the desired polymerizable or initiating functional group. Such macromonomer bifunctional compounds may form polymer stabilizers, which usually contain multiple repeating units of both types.

When selecting a bifunctional compound to provide a polymerizable or initiating functional group on the particles, attention should be paid to the relative positions of the two groups in the reagent. As will be apparent to those skilled in the production of polymers, the rate of reaction of polymerizable or initiating groups attached to a particle depends on whether the group is held tightly and tightly on the surface of the particle, or if this is the chemical reaction of the group. In a more highly favorable environment, it can be very dependent on whether the groups are spaced (on an atomic scale) from their surface and thus extend into the reaction medium surrounding the particles. In general, it is preferable that there are at least 3 atoms in the straight chain between the 2 functional groups.

In an alternative surface treatment method, the composite particles may also be treated by treating the particles with a solution of a reagent having a polymerizable or polymerization initiating group by physically adsorbing a reagent containing a polymerizable group on the surface of the composite particles. Well, this causes the reagent to be physically adsorbed to the particle surface and prevent the reagent from desorbing from the particle surface when the particle is placed in a hydrocarbon medium. This method, disclosed in US Patent Application No. 2015/0218384, is a method in which a composite particle and a reagent physically adsorbed on its surface having at least one monomer or oligomer are placed on the particle having at least one monomer or oligomer. It may further include reacting with the polymerizable or polymerization initiator groups under conditions effective for polymerizing.

For example, in one embodiment, the physisorbent may be dissolved in an ionic solvent or solvent mixture, such as a water / ethanol mixture. The method may include adjusting the pH of the reagent solution to control the charge on the composite particles and selecting the reagent to be physically adsorbed according to the desired charge on the particles. As is well known to those skilled in pigment chemistry, the charge on many pigment particles in an ionic liquid depends on the pH of the liquid, typically at a pH (isoelectric point), where the particles are charged. Not done. Above the isoelectric point of the pigment, the pigment is negatively charged and the reagent may contain a group of quaternary ammonium salts (very often in the method of preparing organoclay), while the isoelectric point. Below, the positively charged pigment surface can be modified by adsorption of reagents containing anionic functional groups. Reagents with a group of quaternary ammonium salts include: [3- (methacryloyloxy) ethyl] trimethylammonium chloride (MAETAC), [3- (methacryloyloxy) ethyl] trimethylammonium methyl sulfate, and [3- (methacryloyl) Amino) propyl] trimethylammonium chloride is included. Reagents with anionic functional groups include 3-sulfopropyl methacrylate potassium salt (SPMK) and sodium 4-vinylbenzene sulfonate. The method is not limited to pigments having an inorganic oxide surface and may, in principle, be extended to any pigment that can be sufficiently charged to promote adsorption of the functionalizing reagent. Reagents that are physically adsorbed on the surface of the pigment particles are preferably composited in a low dielectric constant solvent (typically an aliphatic hydrocarbon) used in the polymerization step and in the internal phase of the final electrophoretic display. It should be chosen to bind to the particles essentially irreversibly.

In another surface treatment method, since the amine group on the surface of the composite particle is nucleophilic, the composite particle can be treated with a reagent which has a polymerizable or polymerization initiating group and also contains at least one electrophilic group. The electrophilic group on the reagent reacts with the nucleophilic group on the particle surface, thus attaching a polymerizable or polymerization initiator group to the particle surface. The method may further comprise reacting the polymerizable or polymerization initiating group with at least one of the monomers or macromonomers described above.

Electrophiles useful in this method include acid halides such as 4-vinylbenzyl chloride and methacryloyl chloride, as well as 2-isocyanatoethyl methacrylate. Both benzyl halides and acid chlorides are highly reactive with respect to nucleophilic substitution reactions. For example, a coupling reaction with 4-vinylbenzyl chloride results in styrene groups anchored to the surface.

In a variant of the surface treatment described above using an electrophile, the reagent may eliminate the polymerizable or polymerization initiating group such that the residue of the reagent chemically bonds to the pigment particles. The reagent may be selected such that the treatment of the composite particles with it affects the zeta potential of the pigment particles. Preferred reagents used in this method are alkyl halides, especially chloride or benzyl bromide. Treatment with either chloride or benzyl bromide shifts the zeta potential of the pigment particles towards a more positive value.

In yet another surface treatment method, by a dispersive polymerization technique such as the method described in US Patent Application No. 2016085132, the entire content of which is then incorporated herein by reference, by applying a silica coating in the first step. The resulting polymer coating may be applied. The polymer coating will act as a steric stabilizer for the composite particles in an electrophoresis medium such as a non-polar solvent.

Various coating methods, such as those described in US Pat. No. 3,639,133, the entire contents of which are incorporated herein by reference, are used to provide composite particles with a silica coating. May be good. Prior to coating the composite particles, the particles may be prepared by first deagglomerating and homogenizing the aqueous slurry of the composite particles using methods such as sonication, ball milling, or jet milling. .. Silica precursors such as sodium silicate or tetraethyl orthosilicate may then be added to the aqueous slurry. In one process, the composite particles are dispersed in a solution of ethanol and tetraethyl orthosilicate and reacted at room temperature for 20 hours under basic conditions to form a nearly uniform coating of silica on the particles and are coated. The silica content of the particles is about 2% to 35% by weight.

After the silica coating has been deposited, the pH of the reaction mixture may be reduced to less than about 4, preferably about 3, after which the silica-coated particles are separated from the reaction mixture. The pH reduction is conveniently carried out using sulfuric acid, but other acids such as nitric acid, hydrochloric acid, and perchloric acid may also be used. The silica-coated particles are conveniently separated from the reaction mixture by centrifugation. After this separation, it is not necessary to dry the particles. Alternatively, the silica-coated particles can be easily redispersed in the medium, typically in an aqueous alcohol medium, and used in the next step of the process to form a polymer on the particles. .. This allows the silica-coated particles to be maintained in a non-aggregated and non-fused form as they are subjected to a dispersion polymerization process for the binding of polymerizable or polymerization initiating groups, and thus by such groups. Allows complete coverage of silica-coated particles and prevents the formation of large aggregates of particles.

During dispersion polymerization, the radically polymerizable group-containing monomer or macromonomer is polymerized around silica-coated particles in the presence of bifunctional reagents. The solvent chosen as the reaction medium must be a good solvent for both the monomer or macromonomer and the bifunctional reagent, but non-solvent for the polymer shell formed. For example, in an aliphatic hydrocarbon solvent of Isopar G®, the monomeric methyl methacrylate is soluble; however, the resulting polymethyl methacrylate after polymerization is not soluble. The polymer coating is derived from various monomer and polymerization techniques known to those of skill in the art, such as those described above (eg, Random Graft Polymerization (RGP), Ionic Random Graft Polymerization (IRGP), and Atom Transfer Radical Polymerization (ATRP)). May be done.

The bifunctional reagent may be a reactive and polymerizable macromonomer that is adsorbed, incorporated, or chemically bonded to the surface of the silica shell and polymer coating. It will be appreciated that since the silica coating completely covers the composite particles, any bifunctional reagent used to attach the initiator or polymerizable group to the surface of the particles must react with the silica coating. .. The bifunctional reagent may be an acrylate-terminated or vinyl-terminated macromolecule, which is suitable because the acrylate or vinyl group can copolymerize with the monomer in the reaction medium that will form the polymer shell. The macromolecule preferably has a long hydrocarbon chain and can stabilize the composite particles in a hydrocarbon solvent.

A preferred type of functional group for binding the bifunctional reagent to the silica-coated particles is a silane coupling group, particularly a trialkoxysilane coupling group. One particularly preferred reagent for attaching polymerizable groups to the silica coating is Dow Chemical Company, Wilmington, Del. 3- (Trimethoxysilyl) propyl methacrylate, which is commercially available under the trade name Z6030. The corresponding acrylate may be used.

One type of macromonomer used as a steric stabilizer is an acrylate-terminated polysiloxane, such as Gelest, MCR-M11, MCR-M17, or MCR-M22. When choosing a bifunctional stabilizer to provide polymerizable or initiating functional groups on the particles, attention should be paid to the relative positions of the two groups in the reagent. As will be apparent to those skilled in the production of polymers, the rate of reaction of polymerizable or initiating groups attached to the particles depends on whether the groups are held tightly and tightly on the surface of the particles, or in addition to the chemical reaction of the groups. Although a very favorable environment, it can be very dependent on whether the groups are spaced (on an atomic scale) from their surface and thus extend into the reaction medium surrounding the particles. In general, it is preferable to have at least 3 atoms in the straight chain between the 2 functional groups; for example, 3- (trimethoxysilyl) propyl methacrylate has 4 atoms between the silyl and the ethylene unsaturated groups. Provides a chain of carbon atoms and one oxygen atom.

According to another embodiment of the invention, the polymer shell on silica-coated organic pigment particles may be prepared by living radical dispersion polymerization. The living radical dispersion polymerization technique is similar to the dispersion polymerization described above by initiating the process by dispersing silica-coated composite particles and monomers and / or macromonomers in a reaction medium. However, in this alternative process, multiple living ends are formed on the surface of the shell. Living terminals use agents such as TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), RAFT (reversible addition-cleavage chain transfer) reagents or the like for living radical polymerization. May be created by adding to the reaction medium.

The second monomer and / or macromonomer added to the reaction medium will react with the living end of the bifunctional reagent to form a polymer coating. The monomer may include any of the monomers or comonomer listed above.

In any of the above processes, the amount of reagents, composite particles, monomers and / or macromonomers used may also be adjusted and controlled to achieve the desired organic content in the resulting composite pigment particles. Good. In addition, the process of the invention may include more than one step and / or more than one type of polymerization.

As described above, the composite pigment of the present invention may be incorporated into an electrophoresis medium used in an electro-optical display. One or more of the composite particles may be dispersed in an encapsulated dispersion fluid, such as a dielectric solvent or solvent mixture. The dispersed fluid may be encapsulated in any method known to those skilled in the art, for example in microcapsules, microcells, or polymer matrices, and in any size or shape, such as spherical, in the millimeter or micron range. It may have a diameter of about tens to about several hundred microns. The percentage of composite particles in the fluid may vary. For example, the particles may make up 0.1% to 50%, preferably 0.5% to 15% of the electrophoretic fluid.

It is desirable that the polymer stabilizer is very compatible with the encapsulated dispersion fluid. In fact, the suspended fluid in the electrophoresis medium is usually hydrocarbon-based and non-polar (eg, C6-C18 branched alkanes), but the fluid increases the density of the fluid and thus of the fluid. It can contain a proportion of halocarbons that are used to reduce the difference between the density and the density of the particles. Therefore, the polymer stabilizers formed in the process of the present invention are very compatible with the encapsulated fluid, and thus the polymer stabilizers themselves can make up most of the hydrocarbon chains. It is important; with the exception of the groups provided for charging purposes, a number of strongly ionic groups make the polymer stabilizer less soluble in hydrocarbon suspension fluids, and thus of the particle dispersion, as discussed below. It is not desirable as it adversely affects stability. Also, as already discussed, the polymer stabilizer is one main chain, at least when the medium in which the particles will be used contains an aliphatic hydrocarbon suspension fluid (as is generally the case). It is advantageous to have a branched or "comb" structure with a chain and multiple side chains extending away from the main chain. Each of these side chains should have at least about 4 carbon atoms, preferably at least about 6 carbon atoms. Substantially long side chains are considered advantageous; for example, some preferred polymer stabilizers may have lauryl (C ₁₂ ) side chains. The side chains may themselves be branched; for example, each side chain may be a branched alkyl group, such as a 2-ethylhexyl group. Due to the high affinity of the hydrocarbon chains for the hydrocarbon-based suspended fluid, the branching of the polymer stabilizer spreads from each other in a brush or dendritic structure through a large volume of liquid, and thus the affinity of the particles for the suspended fluid. It is believed that the sex and the stability of the particle dispersion are increased (but the present invention is not limited to this idea in any way).

There are two basic methods for forming such comb-shaped polymers. The first approach uses monomers that essentially provide the required side chains. Typically, such monomers have a single polymerizable group at one end of the long chain (at least 4, preferably at least 6 carbon atoms). Monomers of this type that have been found to give good results by the methods of the invention include hexyl acrylate, 2-ethylhexyl acrylate, and lauryl methacrylate. Isobutyl methacrylate and 2,2,3,4,5,4-hexafluorobutyl acrylate have also been successfully used. In some cases, it may be desirable to limit the number of side chains formed in such a process, which is a monomer to form a random copolymer in which only some of the repeating units retain long side chains. Can be achieved by using a mixture of (eg, a mixture of lauryl methacrylate and methyl methacrylate). In a second method represented by the RGP-ATRP process, the first polymerization reaction is carried out using a mixture of monomers, at least one of these monomers retains an initiating group and thus such initiation. A first polymer containing a group is produced. The product of this first polymerization reaction is then typically subjected to a second polymerization under conditions different from the first polymerization so that the initiating groups in the polymer are additional to the original polymer. It causes the polymerization of the monomer, thereby forming the desired side chain. As with the bifunctional reagents discussed above, it does not rule out the possibility that some chemical modification of the initiating group may occur between the two polymerizations. In such a process, the side chains themselves do not require severe branching and can be formed from small monomers such as methyl methacrylate.

Free radical polymerization of ethylene-based or similar radically polymerizable groups bonded to particles is carried out at high reaction temperatures, preferably at 60-70 ° C., conventional free radical initiators such as azobis (isobutyryintile). (AIBN) may be used, while ATRP polymerization is carried out by Wang, J. et al. S. , Et al. , Macromolecules 1995, 23, 7901, and J. et al. Am. Chem. Soc. 1995, 117, 5614, and Beers, K. et al. et al. , Macromolecules 1999, 32, 5772-5776, can be carried out using conventional metal complexes. U.S. Pat. Nos. 5,763,548; 5,789,487; 5,807,937; 5,945,491; 4,986,015; 6,069,205; No. 6,071,980; No. 6,111,022; No. 6,121,371; No. 6,124,411; No. 6,137,012; No. 6,153,705; No. 6 , 162,882; 6,191,225; and 6,197,883. The full disclosure of these articles and patents is incorporated herein by reference. A currently preferred catalyst for performing ATRP is copper I chloride in the presence of bipyridyl (Bpy).

The RGP process of the present invention, in which the particles carrying the polymerizable group react with the monomer in the presence of the initiator, is the formation of some "free" polymer that is not attached to the particles because the monomer in the reaction mixture is not polymerized. Will inevitably cause. The unbonded polymer can be obtained by repeated washing of the particles in a solvent (typically a hydrocarbon) in which the unbonded polymer is soluble, or (at least for metal oxides or other dense particles). ) The treated particles are centrifuged from the reaction mixture (with or without solvent or diluent first), the particles are redispersed in a fresh solvent and some of the unbonded polymer is acceptable. It can be removed by repeating these steps until it is reduced to a possible level (after reducing the proportion of unbound polymer, thermal weight analysis of the polymer sample can be performed). Empirically, the presence of a small proportion of unbound polymer, on the order of 1 weight percent, is unlikely to have any serious adverse effects on the electrophoretic properties of the treated particles; in fact, in some cases, they are bound. Depending on the chemistry of the unbonded polymer and the suspended fluid, it is not always necessary to separate the particles with the bonded polymer stabilizer from the unbound polymer before using the particles in the electrophoretic display. it is conceivable that.

As already mentioned, there is an optimal range for the amount of polymer stabilizer to be formed on the electrophoretic particles, and the formation of an excessive amount of polymer on the particles can give them electrophoretic properties. It was found that it could be degraded. The optimum range will vary depending on several factors, including the density and size of the particles to be coated, the nature of the suspension medium in which the particles are intended to be used, and the nature of the polymer formed on the particles. For any particular particle, polymer, and suspension medium, the optimum range is empirically best determined. However, it should be noted that, according to general guidelines, the denser the particles, the lower the optimum ratio of polymer by weight to the particles, and the finer the particles, the higher the optimum ratio of polymer. Should be. In general, the particles should be coated with at least about 2 weight percent, preferably at least about 4 weight percent of the particles. In most cases, the optimum proportion of polymer will range from about 4 to about 15 weight percent of the particles, typically from about 6 to about 15 weight percent, most preferably from about 8 to about 12 weight percent. Percentage.

To incorporate functional groups for charge generation of pigment particles, comonomer may be added to the polymerization reaction medium. The comonomer may directly charge the composite pigment particles or interact with a charge control agent in the display fluid to provide the composite pigment particles with the desired charge polarity and charge density. Suitable comonomers include acrylic acid, methacrylic acid, vinyl phosphate, 2-acrylicamino-2-methylpropanesulfonic acid, 2- (dimethylamino) ethyl methacrylate, N- [3- (dimethylamino) propyl] methacrylamide. , And similar ones may be included. Suitable comonomers include fluorinated acrylates or methacrylates such as 2-perfluorobutylethyl acrylate, 2,2,2 trifluoroethyl methacrylate, 2,2,3,3 tetrafluoropropyl methacrylate, 1, acrylate. 1,1,3,3,3-hexafluoroisopropyl, methacrylic acid 1,1,1,3,3,3-hexafluoroisopropyl, acrylic acid 2,2,3,3,3-pentafluoropropyl, acrylic acid 2,2,3,3-tetrafluoropropyl, 2,2,3,4,4,4-hexafluorobutyl methacrylate, or 2,2,3,3,4,5,4-heptafluorobutyl methacrylate Can also be included. Alternatively, charged or chargeable groups may be incorporated into the polymer via a bifunctional stabilizer used to provide the pigment with polymerizable or initiating functional groups.

Functional groups, such as acidic or basic groups, may be provided in a "blocked" form during polymerization and then unblocked after polymer formation. For example, since ATRP cannot be initiated in the presence of an acid, an ester such as t-butyl acrylate or isobornyl methacrylate may be used if it is desired to provide an acidic group in the polymer, ultimately. The residues of these monomers in the polymer are hydrolyzed to provide acrylic or methacrylic acid residues.

If it is desired to produce charged or chargeable groups on the composite particles and also on the polymer stabilizers individually attached to the particles, a mixture of two reagents, one of which is a mixture of two reagents. Retains a charged or chargeable group (or a group that will eventually be processed to produce the desired charged or chargeable group) and the other retains a polymerizable or polymerization initiating group. It is considered very convenient to treat the particles with the mixture. Desirably, the two reagents are charged or the number of chargeable groups so that the relative rate at which the reagents react with the particles will change in a similar manner if there is slight variation in the reaction conditions. It has the same or essentially the same functional groups that react with the particle surface so that the ratio between and the number of polymerizable or polymerization initiating groups remains substantially constant. It will be appreciated that this ratio can be varied and controlled by varying the relative molarities of the two (or more) reagents used in the mixture.

The density of the electrophoretic particles may substantially match the density of the suspended (ie, electrophoretic) fluid. Suspended fluids as defined herein are "substantially consistent" with particle densities when their density differences are between about zero and about 2 grams / milliliter (“g / ml”). Has density. This difference is preferably between about zero and about 0.5 g / ml.

The solvent in which the composite particles are dispersed may be colorless and transparent. It preferably has a low viscosity and a dielectric constant in the range of about 2 to about 30, preferably about 2 to about 15 with respect to high particle mobility. Examples of suitable dielectric solvents include hydrocarbons such as isopal, decahydronaphthalene (DECALIN), 5-ethylidene-2-norbornene, fatty oils, paraffin oils, silicon fluids, aromatic hydrocarbons such as toluene, xylene, etc. Phenylxylyl ethane, dodecylbenzene, or alkylnaphthalene, halogenating solvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene, dichlorobenzotrifluorides, 3,4,5-trichlorobenzotrifluorides, chloropentafluorobenzene, Dichlorononane, or pentachlorobenzene, and perfluorinated solvents such as 3M Company, St. FC-43, FC-70, or FC-5060 from Paul MN, low molecular weight halogen-containing polymers such as TCI America, Portland, Oregon poly (perfluoropropylene oxide), poly (chlorotrifluoroethylene), eg Halocarbon Product Corp. , River Edge, Halocarbon Oil from NJ, perfluoropolyalkyl ethers such as Galden from Ausimont, or Krytox Oil and grease from DuPon, Delaware, K-Fluid series, polydimethylsiloxane from Dow-Corning (DC-200). Contains silicone oil based on.

Charge control agents may be used with or without charged groups in the polymer coating to provide good electrophoretic mobility to the electrophoretic particles. Stabilizers may be used to prevent agglomeration of electrophoretic particles and to prevent irreversible deposition of electrophoretic particles on the capsule wall. Both components can be composed of a wide range of molecular weight materials (low molecular weight, oligomers or polymers) and may be a single pure compound or mixture. Charge control agents used to modify and / or stabilize particle surface charges are applied as is generally known in the fields of liquid toners, electrophoretic displays, non-aqueous paint dispersions, and engine oil additives. Toner. In all of these areas, charged species may be added to non-aqueous media to increase electrophoretic mobility or electrostatic stabilization. The material can also improve steric stability as well. Various theories of charging are envisioned, including selective ion adsorption, proton transfer, and contact charging.

If necessary, a charge control agent or a charge inducer may be incorporated into the electrophoretic fluid. These components typically consist of low molecular weight surfactants, polymeric agents, or blends of one or more components to stabilize the sign and / or magnitude of charge on the electrophoretic particles. Work to fix it, or in another way. Additional pigment properties that may be associated are particle size distribution, chemical composition, and light resistance.

Charge aids may be added. These materials increase the effectiveness of charge control agents or charge inducers. The charge aid may be a polyhydroxy compound or an aminoalcohol compound and is preferably soluble in the suspended fluid in an amount of at least 2% by weight. Examples of polyhydroxy compounds containing at least two hydroxyl groups include, but are not limited to, ethylene glycol, 2,4,7,9-tetramethyldecine-4,7-diol, poly (propylene). Glyco), pentaethylene glycol, tripropylene glycol, triethylene glycol, glycerol, pentaerythritol, glycerol tris (12-hydroxystearate), propylene glycerol monohydroxystearate, and ethylene glycol monohydroxystearate. Examples of amino alcohol compounds containing at least one alcohol functional group and one amine functional group in the same molecule include, but are not limited to, triisopropanolamine, triethanolamine, ethanolamine, 3-amino. Includes -1-propanol, o-aminophenol, 5-amino-1-pentanol, and tetrakis (2-hydroxyethyl) ethylenediamine. The charge aid is preferably present in the suspended fluid in an amount of about 1 to about 100 milligrams (“mg / g”) per gram of particle mass, more preferably about 50 to about 200 mg / g. ..

It is generally believed that charging is obtained as an acid-base reaction between some part of the continuous phase and the particle surface. Thus, useful materials are capable of engaging in such reactions or any other charging reaction known in the art.

Various non-limiting types of useful charge control agents include organic sulfates or sulfonates, metal soaps, block or comb copolymers, organic amides, organic zwitterions, and organic phosphates and phosphonates. Useful organic sulfates and sulfonates include, but are not limited to, sodium bis (2-ethylhexyl) sulfosuccinate, calcium dodecylbenzenesulfonate, calcium petroleum sulfonate, neutral or basic barium dinonylnaphthalene sulfonate, Includes neutral or basic calcium dinonylnaphthalene sulfonate, sodium dodecylbenzenesulfonic acid salt, and ammonium lauryl sulphate. Useful metal soaps include, but are not limited to, basic or neutral barium petronate, calcium petronate, co-, ca-, Cu-, Mn-, and Ni- of naphthenic acid. −, Zn−−, and Fe−− salts, Ba−− of stearic acid, Al−−, Zn−−, Cu−−, Pb−−, and Fe−− salts, divalent and trivalent metal carboxylates , For example aluminum tristearate, aluminum octanate, lithium heptate, iron stearate, iron distearate, barium stearate, chromium stearate, magnesium octanate, calcium stearate, iron naphthalate, zinc naphthalate, Mn--and Includes Zn --- heptanoates, as well as Ba-, Al-, Co-, Mn-, and Zn --octanoates. Useful block or comb-shaped copolymers include, but are not limited to, (A) a polymer of 2- (N, N-dimethylamino) ethyl methacrylate quaternized with methyl p-toluenesulfonate. (B) AB diblock copolymer with poly (2-ethylhexyl methacrylate), and poly (methyl methacrylate-methacrylic acid) with an oil-soluble tail of (12-hydroxystearic acid) and a molecular weight of about 1800. Includes comb-shaped copolymers, which are the side groups of oil-soluble anchor groups. Useful organic amides include, but are not limited to, polyisobutylene succinimides such as OLOA 371 or 1200 (available from Chevron Oronite Company LLC, Houston, Tex.), Or Solsperse 19000 and Solsperse 17000 (Avecia Lt). , Available from Blackley, Manchester, United Kingdom; "Houston" is a registered trademark), and N-vinylpyrrolidone polymers. Useful organic zwitterions include, but are not limited to, lecithin. Useful organic phosphates and phosphonates include, but are not limited to, sodium salts of phosphorylated mono and diglycerides with saturated and unsaturated acid substituents.

Particle dispersion stabilizers may be added to prevent particle agglutination or binding to the capsule wall. Non-aqueous surfactants may be used in typical high resistivity liquids used as suspension fluids for electrophoretic displays. These include, but are not limited to, glycol ethers, acetylene glycols, alkanolamides, sorbitol derivatives, alkylamines, quaternary amines, imidazolines, dialkyl oxides, and sulfosuccinates.

If a bistable electrophoresis medium is desired, it may be desirable to include a polymer in the suspended fluid with a number average molecular weight greater than about 20,000, which polymer is essential for the electrophoresis particles. Non-absorbent, poly (isobutylene) is the preferred polymer for this purpose. See U.S. Pat. No. 7,170,670, the entire disclosure of which is incorporated herein by reference.

The following examples are shown as exemplary embodiments of the invention and do not limit the scope of the invention.

Step 1:

Sample 1

About 2 g of Solvent Blue 70 was dissolved in a solution of 10 g of Bayhydr 302 and 10 g of tetrahydrofuran (THF) at room temperature (about 20 ° C.). The solution was then added under the surface to a stirring flask containing deionized water (100 g) using a pipette at 25 ° C. The mixture thus formed was stirred overnight, then centrifuged (3500 rpm for 30 minutes) and then the supernatant was decanted. The resulting cake of stained particles was air dried and then crushed with a spatula.

Sample 2

The same process as in Example 1 was repeated, except that 2 g of Orasol Yellow GLN was used in place of Solvent Blue 70.

Step 2:

4.5 g of Samples 1 and 2 were individually combined with Isopar-E (18 g) and Solspace 17k (4.5 g of 20% solution in isopar-E) in a glass jar containing a magnetic stirring bar. 3 mm diameter glass beads (20 g) were added and the mixture was stirred overnight to give a slurry of small stained particles.

Microscopic analysis of the slurry revealed particles ranging in size from about 0.5 to 5 microns.

Although preferred embodiments of the present invention have been shown and described herein, it will be appreciated that such embodiments are provided by way of example only. A number of variants, modifications, and substitutions will be conceived by those skilled in the art without departing from the spirit of the invention. Accordingly, the appended claims shall include all such variations within the spirit and scope of the invention.

Claims (20)

It contains a base particle and a plurality of hydrophilic oligomeric groups on the outer portion of the base particle, the base particle contains a crosslinked polyurea and at least one of a pigment and a dye, and the crosslinked polyurea is the base. Composite particles that form a network of particles throughout. The composite particle according to claim 1, wherein the hydrophilic oligomer group is an aliphatic. The composite particle according to claim 2, wherein the hydrophilic oligomer group contains polyethylene oxide. The composite particle according to claim 1, wherein the dye is insoluble in water and soluble in a water-miscible solvent. The dyes are Solvent Blue 70, Solvent Blue 67, Solvent Blue 136, Solvent Red 127, Solvent Red 130, Solvent Red 233, Solvent Red 125, Solvent Red 122, Solvent Yellow6 89, Solvent Orange 11, Solvent Orange 99, Solvent Brown 42, Solvent Brown 43, Solvent Brown 44, Solvent Black 28, Solvent Black 29, and a compound according to a combination thereof. .. The composite particle according to claim 1, wherein the outer portion of the base particle further contains an amino group. An electrophoresis medium containing the composite particles according to claim 1 and a non-polar fluid. The electrophoresis medium according to claim 7, wherein the non-polar fluid contains C6-C18 branched alkanes. A method of producing composite particles
Dissolving the dye and water-dispersible polyfunctional isocyanate in a water-miscible solvent to form a solution,
Adding the solution to the aqueous phase to form an emulsion,
A method comprising stirring the emulsion while the polyfunctional isocyanate is converted to crosslinked polyurea, and separating composite particles containing the crosslinked polyurea and the dye from the emulsion. The method according to claim 9, wherein the water-dispersible polyfunctional isocyanate contains a hydrophilic oligomer group and at least one isocyanate group. The method according to claim 10, wherein the hydrophilic oligomer group is an aliphatic. The method of claim 10, wherein the hydrophilic oligomer group comprises polyethylene oxide. The method of claim 9, wherein the water-miscible solvent has a water solubility of at least 25% by weight. 13. The method of claim 13, wherein the water-miscible solvent is selected from the group consisting of THF, methyl acetate, and mixtures thereof. A method of producing composite particles
Dispersing the pigment in a solution containing a water-dispersible polyfunctional isocyanate dissolved in a water-miscible solvent to form a dispersion,
Adding the dispersion to the aqueous phase to form an emulsion,
A method comprising stirring the emulsion while the polyfunctional isocyanate is converted to crosslinked polyurea, and separating composite particles containing the crosslinked polyurea and the pigment from the emulsion. The method according to claim 15, wherein the water-dispersible polyfunctional isocyanate contains a hydrophilic oligomer group and at least one isocyanate group. 16. The method of claim 16, wherein the hydrophilic oligomeric group is aliphatic. 16. The method of claim 16, wherein the hydrophilic oligomeric chain comprises polyethylene oxide. 15. The method of claim 15, wherein the water-miscible solvent has a water solubility of at least 25% by weight. 19. The method of claim 19, wherein the water-miscible solvent is selected from the group consisting of THF, methyl acetate, and mixtures thereof.

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