An electrophoretic medium comprising particles having a pigment core and a polymeric shell

Abstract

An electrophoretic medium is disclosed, comprising a plurality of first-type particles, a plurality of second-type particles, and a nonpolar liquid. Each of the plurality of first-type particles has a core and a shell. The core comprises a pigment. The shell of the first-type particle comprises a polymer, which is a homopolymer or copolymer. The homopolymer is formed from vinylnaphthalene, and the copolymer is formed from vinylnaphthalene and a first monomer.

Description

Technical Field

[0001] Related applications This application claims priority to U.S. Provisional Patent Application No. 63 / 617,957, filed January 5, 2024, the entire contents of which, together with all other patents and patent applications disclosed herein, are incorporated herein by reference.

[0002] Invention Field This invention relates to particles comprising a core and a shell, the core containing a pigment and the shell containing a polymer formed of vinylnaphthalene. These particles can be used in electrophoretic media of electro-optic devices. Prior Technology

[0003] When applied to materials, devices, or displays, the term "electro-optic" is used here in its familiar sense in imaging technology, referring to a material having different first and second display states in at least one optical property, which is altered from its first to its second display state by applying an electric field to the material. While this optical property is typically color that can be distinguished by the human eye, it can be another optical property, such as light transmittance, reflectivity, luminescence; or, in the case of a display intended for machine reading, false color in the sense of a change in reflectivity at electromagnetic wavelengths outside the visible light range.

[0004] 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. For convenience, displays using such solid-state electro-optic materials will henceforth be referred to as "solid-state electro-optic displays." Therefore, the term "solid-state electro-optic display" includes rotating dual-color component displays, encapsulated electrophoretic displays, microcellular electrophoretic displays, and encapsulated liquid crystal displays.

[0005] The terms "bistable" and "bistable" are used herein in their art-known sense, referring to a display comprising display elements having at least one optically distinct first and second display states, such that after any provided element has been driven to its assumed first or second display state by an addressing pulse of a finite duration, the state remains for a period of time after the addressing pulse has terminated, which is at least several times, for example, at least four times, the minimum period of the addressing pulse required to change the state of the display element. It has been shown in U.S. Patent No. 7,170,670 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 that some other types of electro-optic displays have the same property. Although for convenience the term "bistable" may be used herein to encompass both bistable and multistable displays, this type of display is properly referred to as "multistable" rather than bistable.

[0006] 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 with liquid crystal displays (LCDs), electrophoretic displays offer advantages such as good brightness and contrast, wide viewing angles, state bistableness, and low power consumption. However, long-term image quality issues have hindered their widespread use. For example, the particles constituting an electrophoretic display tend to settle, leading to a shorter lifespan for these displays.

[0007] As mentioned above, the electrophoretic medium requires the presence of a fluid. In most prior art electrophoretic media, this fluid system is liquid, but a gaseous fluid can be used to manufacture the electrophoretic medium; see, for example, 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. Patent Nos. 7,321,459 and 7,236,291. When the medium is used in an orientation that allows for this sedimentation, for example, in a signboard in a vertical plane, this gas-based electrophoretic medium appears to be susceptible to the same type of problems due to particle sedimentation as liquid-based electrophoretic media. More precisely, particle sedimentation in gas-based electrophoretic media exhibits more severe problems than in liquid-based media because the lower viscosity of gaseous suspensions allows for faster electrophoretic particle sedimentation compared to liquids.

[0008] Numerous patents and applications belonging to or in the name of the Massachusetts Institute of Technology (MIT), E Ink Corporation, E Ink California, LLC, and related companies describe various techniques used in encapsulated and microelectrophoretic media and other electro-optic media. These encapsulated electrophoretic media comprise a plurality of microcapsules, each containing an inner phase of electrophoretically moving particles in a fluid medium, and a capsule wall surrounding the inner phase. Typically, these capsules are themselves housed within a polymer binder to form a coherent layer between two electrodes. In microelectrophoretic displays, the charged particles and the fluid are not encapsulated within microcapsules, but rather retained within a plurality of cavities formed in a carrier medium, typically a polymer membrane. The techniques described in these patents and applications include:

[0009] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, U.S. Patent 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; 6,538,801; 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;7,038,655;7,052,766;7,110,162;7,113,323;7,141,688;7,142,351;7,170,670;7,226,550;7,230,750;7,230,751;7,236,290;7,277, 218;7,286,279;7,312,916;7,382,514;7,390,901;7,473,782;7,561,324;7,583,251;7,572,394;7,576,904;7,580,180;7,679,814;7,848,006;7 ,903,319;8,018,640;8,115,729;8,257,614;8,270,064;8,363,306;8,390,918;8,582,196;8,654,436;8,902,491;8,961,831;9,052,564;9,341, 915;9,348,193;9,361,836;9,366,935;9,372,380;9,382,427;9,423,666;9,428,649;9,557,623;9,670,367;9,671,667;9,688,859;9,726,957;9 ,752,034;9,765,015;9,778,535;9,778,537;9,835,926;9,953,588;9,995,987;10,025,157;10,031,394;10,040,954;10,061,123;10,062,337;1 0,147,366; and 10,514,583; and U.S. Patent Application Publication Nos. 2003 / 0048522; 2003 / 0151029; 2003 / 0164480; 2004 / 0030125; 2004 / 0105036; 2005 / 0012980; 2009 / 0009852;2011 / 0217639; 2012 / 0049125; 2013 / 0161565; 2013 / 0193385; 2013 / 0244149; 2013 / 0063333; 2014 / 0011913; 2014 / 0078576; 2014 / 0104674; 2014 / 0231728; 2015 / 0177590; 2015 / 0185509; 2015 / 0241754; 2015 / 0301425; and 2016 / 0170106.

[0010] (b) Capsules, adhesives, and encapsulation methods; see, for example, U.S. Patent Nos. 5,930,026; 6,067,185; 6,130,774; 6,262,706; 6,327,072; 6,392,786; 6,459,418; 6,727,881; 6,839,158; 6,866,760; 6,922,276; 6,958,848; 6,987,603; 7,110,164; 7,1 48,128;7,184,197;7,304,634;7,327,511;7,339,715;7,411,719;7,477,444;7,561,324;7,910,175;7,952,790;8,129,655;8,446,664; and U.S. Patent Application Publication Nos. 2005 / 0156340; 2007 / 0091417; and 2009 / 0122389.

[0011] (c) Microcellular structures, wall materials, and methods for forming microcells; see, for example, U.S. Patent Nos. 6,672,921; 6,751,007; 6,753,067; 6,781,745; 6,788,452; 6,795,229; 6,806,995; 6,829,078; 6,850,355; 6,865,012; 6,870,6 62;6,885,495;6,930,818;6,933,098;6,947,202;7,046,228;7,072,095;7,079,303;7,141,279;7,156,945;7,205,355;7,233,429;7,261,920;7,271,947;7,304, 780;7,307,778;7,327,346;7,347,957;7,470,386;7,504,050;7,580,180;7,715,087;7,767,126;7,880,958;8,002,948;8,154,790;8,169,690;8,441,432;8,891 ,156;9,279,906;9,291,872;9,388,307;9,436,057;9,436,058;9,470,917;9,919,553; and 10,401,668; and U.S. Patent Application Publication Nos. 2003 / 0203101; 2014 / 0050814; and 2016 / 0059442.

[0012] (d) A method for filling and sealing microcells; see, for example, U.S. Patent Nos. 6,545,797; 6,788,449; 6,831,770; 6,833,943; 6,930,818; 7,046,228; 7,052,571; 7,166,182; 7,347,957; 7,374,634; 7,385,751; 7,408,696; 7,557,981; 7,560,004 ;7,564,614;7,572,491;7,616,374;7,715,087;7,715,088;8,361,356;8,625,188;8,830,561;9,346,987; and 9,759,978; and U.S. Patent Application Publication Nos. 2002 / 0188053; 2004 / 0120024; 2004 / 0219306; and 2015 / 0098124.

[0013] (e) Films and sub-components containing electro-optic materials; see, for example, U.S. Patent Nos. 6,825,829; 6,982,178; 7,110,164; 7,158,282; 7,554,712; 7,561,324; 7,649,666; 7,728,811; 7,826,129; 7,839,564; 7,843,6 21; 7,843,624; 7,952,790; 8,034,209; 8,177,942; 8,390,301; 9,238,340; 9,470,950; 9,835,925; and U.S. Patent Application Publication Nos. 2005 / 0122563; 2007 / 0237962; and 2011 / 0164301.

[0014] (f) Backplanes, adhesive layers, and other auxiliary layers and methods used in displays; see, for example, U.S. Patent Nos. D485,294;5,930,026;6,120,588;6,124,851;6,177,921;6,232,950;6,252,564;6,312,304;6,312,971;6,376,828;6,392,786;6,413,790;6,480,182;6,498,114;6,506,438;6,518,949;6,545,291;6,639,578;6,657,772;6,664,944;6,683,333;6 710,540;6,724,519;6,816,147;6,819,471;6,825,068;6,831,769;6,842,279;6,842,657;6,865,010;6,873,452;6,909,532;6,967,640;7,012,6 00;7,012,735;7,030,412;7,075,703;7,106,296;7,110,163;7,116,318;7,148,128;7,167,155;7,173,752;7,176,880;7,190,008;7,206,119;7, 223,672;7,230,751;7,256,766;7,259,744;7,301,693;7,304,780;7,327,346;7,327,511;7,347,957;7,365,733;7,388,572;7,401,758;7,492,4 97;7,535,624;7,551,346;7,554,712;7,560,004;7,583,427;7,649,674;7,667,886;7,672,040;7,688,497;7,826,129;7,830,592;7,839,564;7, 880,958;7,893,435;7,905,977;7,952,790;7,986,450;8,034,209;8,049,947;8,072,675;8,120,836;8,159,636;8,177,942;8,237,892;8,362,4 88;8,395,836;8,437,069;8,441,414;8,456,589;8,514,168;8,547,628;8,576,162;8,610,988;8,714,780;8,743,077;8,754,85​​9;8,797,258;8,797,633;8,797,636;9,147,364;9,025,234;9,025,238;9,030,374;9,140,​​952;9,201,279;9,223,164;9,238,340;9,285,648;9,454,057;9,529,240;9,620,066; 9,632,373;9,666,142;9,671,635;9,715,155;9,777,201;9,897,891;10,037,735;10,190,743;10,324,577;10,365,533;10,372,008;10,446,585;10,466,565;10,495 ,941;10,503,041;10,509,294;10,613,407; and U.S. Patent Application Publication Nos. 2002 / 0060321;2004 / 0085619;2004 / 0105036;2005 / 0122306;2005 / 0122563;2006 / 0255322;2009 / 0122389;20 10 / 0177396; 2011 / 0164301; 2011 / 0292319; 2014 / 0192000; 2014 / 0210701; 2014 / 0368753; and 2016 / 0077375; and international application publication numbers WO2000 / 038000; WO2000 / 005704; and WO1999 / 067678.

[0015] (g) Color formation and color adjustment; see, for example, U.S. Patent Nos. 6,017,584; 6,545,797; 6,664,944; 6,788,452; 6,864,875; 6,914,714; 6,972,893; 7,038,656; 7,038,670; 7,046,228; 7,052,571; 7,075,502; 7,167,155; 7,385,751; 7,492,505; 7,667,684; 7,684,108; 7,791,789; 7,800,813; 7,821,702; 7,839,564; 7,910,175; 7,952 ,790;7,956,841;7,982,941;8,040,594;8,054,526;8,098,418;8,159,636;8,213,076;8,363,299;8,422,116;8,441,714;8,441,716;8,466,852 ;8,503,063;8,576,470;8,576,475;8,593,721;8,605,354;8,649,084;8,670,174;8,704,756;8,717,664;8,786,935;8,797,634;8,810,899;8,83 0,559;8,873,129;8,902,153;8,902,491;8,917,439;8,964,282;9,013,783;9,116,412;9,146,439;9,164,207;9,170,467;9,170,468;9,182,646;9,195,111;9,199,441;9,268,191;9,285,649;9,293,511;9,341,916;9,360,733;9,361,836;9,383,623; and 9,423,666; and U.S. Patent Application Publication No. 2008 / 00433 18;2008 / 0048970;2009 / 0225398;2010 / 0156780;2011 / 0043543;2012 / 0326957;2013 / 0242378;2013 / 0278995;2014 / 0055840;2014 / 0078576;2014 / 0340430;2014 / 0340736;2014 / 0362213;2015 / 0103394;2015 / 0118390;2015 / 0124345;2015 / 0198858;2015 / 0234250;2015 / 0268531;2015 / 0301246;2016 / 0011484; 2016 / 0026062; 2016 / 0048054; 2016 / 0116816; 2016 / 0116818; and 2016 / 0140909.

[0016] (h) A method for driving a display; see, for example, U.S. Patent Nos. 5,930,026; 6,445,489; 6,504,524; 6,512,354; 6,531,997; 6,753,999; 6,825,970; 6,900,851; 6,995,550; 7,012,600; 7,023,420; 7,034,783; 7,061,166; 7,061,662; 7,116,466; 7,119,772; 7,177,066; 7,193,625; 7,202,847; 7,242,514; 7,259,744; 7,304,787; 7 ,312,794;7,327,511;7,408,699;7,453,445;7,492,339;7,528,822;7,545,358;7,583,251;7,602,374;7,612,760;7,679,599;7,679,813;7,68 3,606;7,688,297;7,729,039;7,733,311;7,733,335;7,787,169;7,859,742;7,952,557;7,956,841;7,982,479;7,999,787;8,077,141;8,125,5 01;8,139,050;8,174,490;8,243,013;8,274,472;8,289,250;8,300,006;8,305,341;8,314,784;8,373,649;8,384,658;8,456,414;8,462,102; 8,514,168;8,537,105;8,558,783;8,558,785;8,558,786;8,558,855;8,576,164;8,576,259;8,593,396;8,605,032;8,643,95;8,665,206;8,68 1,191;8,730,153;8,810,525;8,928,562;8,928,641;8,976,444;9,013,394;9,019,197;9,019,198;9,019,318;9,082,352;9,171,508;9,218,7 73;9,224,338;9,224,342;9,224,344;9,230,492;9,251,736;9,262,973;9,269,311;9,299,294;9,373,289;9,390,066;9,390,661;and9,412,314;and U.S. patent application publication numbers 2003 / 0102858; 2004 / 0246562; 2005 / 0253777; 2007 / 0091418; 2007 / 0103427; 2007 / 0176912; 2008 / 0024429; 2008 / 0024482; 2008 / 0136774; 2008 / 0291129; 2008 / 0303780; 2009 / 0174651; 2009 / 0195568;2 009 / 0322721;2010 / 0194733;2010 / 0194789;2010 / 0220121;2010 / 0265561;2010 / 0283804;2011 / 0063314;2011 / 0175875;2011 / 0193840;2011 / 0193841;2011 / 0199671;2011 / 0221740;2012 / 0001957;2012 / 0098740;2 013 / 0063333;2013 / 0194250;2013 / 0249782;2013 / 0321278;2014 / 0009817;2014 / 0085355;2014 / 0204012;2014 / 0218277;2014 / 0240210;2014 / 0240373;2014 / 0253425;2014 / 0292830;2014 / 0293398;2014 / 0333685;2 014 / 0340734; 2015 / 0070744; 2015 / 0097877; 2015 / 0109283; 2015 / 0213749; 2015 / 0213765; 2015 / 0221257; 2015 / 0262255; 2015 / 0262551; 2016 / 0071465; 2016 / 0078820; 2016 / 0093253; 2016 / 0140910; and 2016 / 0180777.

[0017] (i) Applications of displays; see, for example, U.S. Patent Nos. 6,118,426; 6,473,072; 6,704,133; 6,710,540; 6,738,050; 6,825,829; 7,030,854; 7,119,759; 7,312,784; 7,705,824; 8,009,348; 8,011,592; 8,064,962; 8,162,212; 8,553,012; 8,973,837; 9,188,82 9; and 9,197,704; and U.S. Patent Application Publication Nos. 2002 / 0090980; 2004 / 0119681; 2007 / 0285385; 2013 / 0176288; 2013 / 0221112; 2013 / 0233930; 2013 / 0235536; 2014 / 0049808; 2014 / 0062391; 2014 / 0206292; and 2016 / 0035291; and International Application Publication No. WO00 / 36560.

[0018] (j) Non-electrophoretic displays, such as those described in U.S. Patent Nos. 6,241,921; 6,784,953; 6,795,138; 6,914,713; 6,950,220; 7,095,477; 7,182,830; 7,245,414; 7,420,549; 7,471,369; 7,576,904; 7,580,180; 7,850,867; 8,018,643; 8,023,071; 8,282,762; 8,319,759; and 8, See, for example, U.S. Patent Application Publications 2005 / 0099575; 2006 / 0262249; 2007 / 0042135; 2007 / 0153360; 2008 / 0020007; 2012 / 0293858; and 2015 / 0277160; and applications of encapsulation and microcell technology other than displays, see, for example, U.S. Patent No. 7,615,325; and U.S. Patent Application Publications 2015 / 0005720 and 2016 / 0012710.

[0019] 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, thus producing a so-called polymer dispersion electrophoretic display, wherein the electrophoretic medium comprises a plurality of discrete electrophoretic fluid droplets and a continuous polymeric material phase, and the discrete electrophoretic fluid droplets within this polymer dispersion electrophoretic display can be considered as capsules or microcapsules even without discrete capsule films associated with each individual droplet; see, for example, the aforementioned U.S. Patent No. 6,866,760. Therefore, for the purposes of this application, this polymer dispersion electrophoretic medium is considered a subtype of encapsulated electrophoretic media.

[0020] Although electrophoretic media are often opaque (because, for example, in many electrophoretic media, these particles substantially impede visible light from passing through the display) and operate in reflective mode, many electrophoretic displays can operate in so-called "shutter mode," in which one display state is substantially opaque and another is translucent. See, for example, U.S. Patent Nos. 5,872,552, 6,130,774, 6,144,361, 6,172,798, 6,271,823, 6,225,971, and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely on changes in electric field strength, can operate in a similar mode; see U.S. Patent No. 4,418,346. Other types of electro-optic displays may also operate in shutter mode. In the multi-layer structure of a full-color display, an electro-optic medium operating in shutter mode can 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.

[0021] Encapsulated electrophoretic displays typically do not suffer from the clustering and settling failure modes of conventional electrophoresis devices, and offer further advantages such as the ability to print or coat displays on a wide 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 coating, such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating, such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; screen printing; electrostatic printing; thermal printing; inkjet printing; electrophoretic deposition (see U.S. Patent No. 7,339,715); and other similar techniques.) Therefore, the resulting display is flexible. Furthermore, because the display medium can be printed (using various methods), the display itself can be manufactured inexpensively.

[0022] Image quality in electrophoresis apparatuses containing electrophoretic media with charged pigment particles in nonpolar liquids can be degraded due to the aggregation of charged particles in the electrophoretic media, particularly in the case of organic pigments. This aggregation can occur between charged particles of the same type or between charged pigment particles of different types. For example, the electrophoretic media may contain charged particles of four different colors, such as blue, red, yellow, and white. In this electrophoretic media, aggregation between blue-red and blue-yellow particles prevents complete separation between the electrophoretic particles during device operation, resulting in fewer color states in the device. Similarly, electrophoretic media may contain charged particles containing cyan, magenta, yellow, and white pigments, and aggregation can occur between cyan-magenta, cyan-yellow, and magenta-yellow, which has a detrimental effect on the electro-optical performance of the device. Aggregation between organic pigment particles can be slightly reduced if one or more of these organic pigments, such as cyan or blue pigments, are replaced by inorganic pigments with similar color properties. However, compared to organic pigments, inorganic pigments generally cannot provide colors with high chromaticity. Therefore, there is a need to improve the particles used in electrophoretic media. Furthermore, the image initially formed by an electro-optic device can change over time. For example, the white state of the device can shift to a slightly paler white state, which degrades the overall image quality. Therefore, there is a need to design electrophoretic particles that contribute to a more stable optical state in the electrophoretic medium. The inventors of this invention have surprisingly discovered that by using particles comprising (1) a core containing pigment particles and (2) a shell containing a polymer formed from monomers (wherein the monomeric system is vinylnaphthalene), the electro-optic performance of the corresponding device is significantly improved by providing more color states and optical states that are more stable over time.

[0023] One of the problems occasionally observed in electrophoretic displays under certain conditions is "image retention." This occurs when a type of electrophoretic particle is strongly adsorbed onto the surface of microcells in the electro-optic material layer and is not completely removed after an electric field is applied, preventing the microcells from effectively switching from a first color state to a second color state. In this case, the second color state is contaminated by the first color state, degrading the image quality of the electro-optic display. Historically, this problem has been mitigated by using electrophoretic media that include filler particles in addition to the electrophoretic charged particles (see U.S. Patent 8,115,729 B2). However, the inclusion of filler particles also increases the viscosity of the electrophoretic medium, increases the switching speed between color states, and increases the voltage required for switching between optical states. The inventors of this invention have surprisingly discovered that the corresponding electrophoretic particles can be surface-treated with a polymer formed from vinyl naphthalene monomer and polydimethylsiloxane macromonomer to reduce image residue without affecting the viscosity of the electrophoretic medium, wherein the polymer has a weight average molecular weight greater than 55,000 dUTP. Summary of the Invention

[0024] According to one embodiment of the invention, the electrophoretic medium comprises a nonpolar liquid, a plurality of first-type particles, and a plurality of second-type particles. Each of the plurality of first-type particles comprises a core and a shell. The core comprises a pigment having a surface; the pigment is an organic or inorganic pigment. The shell comprises a polymer, which is a homopolymer or copolymer. The homopolymer is formed from vinylnaphthalene. The copolymer is formed from vinylnaphthalene and a first monomer. The homopolymer or copolymer is in contact with the surface of the pigment. The polymer of the shell may have a weight average molecular weight of 55,000 to 500,000 Da, 55,000 to 400,000 Da, 55,000 to 300,000 Da, 55,000 to 350,000 Da, 55,000 to 300,000, 55,000 to 250,000, or 55,000 to 200,000 Da. The polymer of the shell can have a weight average molecular weight greater than 55,000.

[0025] The vinylnaphthalene can be 1-vinylnaphthalene, 2-vinylnaphthalene, substituted 1-vinylnaphthalene, and substituted 2-vinylnaphthalene, wherein the substituted 1-vinylnaphthalene and the substituted 2-vinylnaphthalene have one or more substituents in addition to the vinyl substituent on the aromatic carbon of the naphthalene ring. The one or more substituents can be selected from the group consisting of: halogen, alkoxy, alkyl, nitro, carboxyl, hydroxyl, sulfonic group, sulfonate group, and amino.

[0026] The first monomer may be a macromonomer. The macromonomer may have a molecular structure including a first functional group and a second functional group. The first functional group may be polydimethylsiloxane and the second functional group may be vinyl, methacrylate, or acrylate.

[0027] The first monomer may have a molecular structure comprising functional groups selected from the group consisting of vinyl, acrylate, and methacrylate groups. The first monomer may be selected from the group consisting of: methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, ethylhexyl methacrylate, ethylhexyl acrylate, lauryl methacrylate, lauryl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,2-trifluoroethyl acrylate, styrene, and α-methylstyrene.

[0028] The copolymer may be formed from the vinylnaphthalene, the first monomer and the second monomer, wherein the first monomer is 2,2,2-trifluoroethyl methacrylate, and the second monomer has a molecular structure including (i) polydimethylsiloxane and (ii) vinyl functional groups, acrylate functional groups or methacrylate functional groups, wherein the copolymer may have a weight average molecular weight of 55,000 to 250,000 Da, 55,000 to 200,000 Da, or 55,000 to 180,000 Da. The copolymer can be formed from vinylnaphthalene, the first monomer, and the second monomer, wherein the first monomer is 2,2,2-trifluoroethyl methacrylate, and the second monomer is a monomethacrylic acid oxypropyl-terminated polydimethylsiloxane, wherein the copolymer can have a weight average molecular weight of 55,000 to 250,000 Da, 55,000 to 200,000 Da, or 55,000 to 180,000 Da. The copolymer can be formed from vinylnaphthalene, the first monomer, the second monomer, and the third monomer.

[0029] The electrophoretic medium may also contain a plurality of third-type particles and a plurality of fourth-type particles. The first and second-type particles may contain organic pigments, the third-type particles may contain organic pigments, and the fourth-type particles may contain inorganic pigments. The first, second, and third-type particles may have a first charge polarity, and the fourth-type particles may have a second charge polarity, wherein the first charge polarity may be opposite to the second charge polarity.

[0030] The first, second, and third types of particles can be independently selected from the group consisting of cyan, magenta, yellow, blue, green, and red, and the fourth type of particle is white.

[0031] The first, second, and third types of particles can be independently selected from the following groups: azo pigments, phthalocyanine pigments, quinacrine pigments, perylene pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, isoindoline pigments, anthrone pigments, indanthrone pigments, rhodamine pigments, benzinamine pigments, carbon black pigments, and mixtures thereof.

[0032] The first, second, and third types of particles can be independently selected from the following groups: 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 Pigment 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 Pigment Green 7 and 36; CI Pigment Black 1 and 7; CI Pigment Brown 25, 32, and 41; Pigment Orange 5, 13, 34, 36, 38, 43, 61, 62, 64, 68, 67, 72, 73, and 74; and mixtures thereof.

[0033] The electrophoretic medium may contain particles of types one, two, three, four, and five. The fifth type of particles may contain inorganic or organic pigments. The first and fourth types of particles may have a charge polarity opposite to that of the second, third, and fifth types of particles. The first and fourth types of particles may carry a negative charge, while the second, third, and fifth types of particles may carry a positive charge. If the first and fourth types of particles are negatively charged, the first type of particle may have a more negative zeta potential than the fourth type of particle. If the second, third, and fifth types of particles are positively charged, the fifth type of particle may have a greater zeta potential than the second and third types of particles. The color of the fourth and fifth types of particles may be selected from the group consisting of white and black.

[0034] According to another embodiment of the invention, the electro-optic device comprises a first transparent electrode layer, an electro-optic material layer comprising the electrophoretic medium, and a second electrode layer. The electrophoretic medium comprises a nonpolar liquid, a plurality of first-type particles, and a plurality of second-type particles. Each of the plurality of first-type particles comprises a core and a shell. The core comprises a pigment having a surface, and the shell comprises a polymer, which is a homopolymer or copolymer. The homopolymer is formed from vinylnaphthalene. The copolymer is formed from vinylnaphthalene and a first monomer. The homopolymer or copolymer is in contact with the surface of the pigment. The vinylnaphthalene may be 1-vinylnaphthalene, 2-vinylnaphthalene, substituted 1-vinylnaphthalene, and substituted 2-vinylnaphthalene, wherein the substituted 1-vinylnaphthalene and the substituted 2-vinylnaphthalene have one or more substituents in addition to the vinyl substituent on the aromatic carbon of the naphthalene ring. The one or more substituents may be selected from the group consisting of: halogen, alkoxy, alkyl, nitro, carboxyl, hydroxy, sulfonic acid, sulfonate and amino.

[0035] According to another aspect of the present invention, a method for manufacturing an electrophoretic medium comprising a nonpolar liquid and a plurality of first-type particles having a core and a shell, the method comprising the following steps: (a) providing a first dispersion comprising an organic pigment in a first organic solvent; (b) adding vinylnaphthalene, a first monomer, and a free radical initiator to the first dispersion and mixing to form the first-type shell particles; (c) washing the first-type particles with a second organic solvent; and (d) dispersing the washed particles in the nonpolar liquid. The first dispersion may further comprise a charge control agent. The method may further comprise the step of adding the charge control agent to the dispersion of the washed particles in the nonpolar liquid. The method may further comprise the step of adding a second dispersion comprising organic or inorganic pigments in the nonpolar liquid to the dispersion of the washed particles in the nonpolar liquid.

[0036] Various forms and specific examples of this application will be illustrated with reference to the following diagrams. It should be understood that these diagrams are not necessarily drawn to scale. Simple Explanation of the Diagram

[0037] Figure 1 is a side view of a portion of an electro-optic device, which includes an electrophoretic medium encapsulated in a plurality of microcapsules. The device includes a first transparent electrode layer, an electrophoretic material layer, a first adhesive layer, and a second electrode layer.

[0038] Figure 2 is a side view of a portion of an electro-optic device, which includes an electrophoretic medium encapsulated in a plurality of microcapsules. The device includes a first transparent electrode layer, a second adhesive layer, an electrophoretic material layer, the first adhesive layer, and the second electrode layer.

[0039] Figure 3 is a side view of a portion of an electro-optic device, which includes an electrophoretic medium encapsulated in a plurality of microcapsules. The device includes a first transparent electrode layer, a microcell layer, an adhesive layer, and a second electrode layer.

[0040] Figure 4 shows a method for producing microcells for use in this invention using a roll-to-roll method.

[0041] Figures 5A and 5B detail the production of microcells for electro-optic devices using photolithography exposure through a photomask coated with a thermosetting precursor.

[0042] Figures 5C and 5D detail alternative specific examples of using photolithography to fabricate microcells for electro-optic devices. In Figures 5C and 5D, a combination of top and bottom exposure is used, such that the partition wall in one lateral direction is cured by exposure of the top photomask; and the partition wall in another lateral direction is cured by bottom exposure through the opaque substrate conductor film.

[0043] Figures 6A-6D illustrate the steps of filling and sealing the microcell array to be used in an electro-optical device. Implementation

[0044] Detailed description of the invention "Dispersion polymerization" is a polymerization process involving soluble starting materials (including monomers, initiators, etc.), in which the polymer product is precipitated during the polymerization process. In the case of the manufacturing process of electrophoretic core-shell particles, the polymerization is carried out in a pigment dispersion, which allows the polymer formed by dispersion polymerization to precipitate on the surface of the pigment particles.

[0045] The term "homogeneous polymer" refers to a polymer containing only one type of repeating unit. Therefore, homopolymers are typically formed from one type of monomer.

[0046] The term "vinylnaphthalene" refers to a molecule containing a vinyl group bonded to an aromatic carbon atom in the naphthalene aromatic system. This naphthalene aromatic system is represented by Formula 1. Formula 1 comprises a fused aromatic ring system with ten aromatic carbon atoms. The conventional numbering of the carbon atoms in the naphthalene is provided in Formula 1. The vinyl group is represented by Formula 2. A simpler equivalent representation of vinyl is: -CH=CH2.

[0047] The term "substituted 1-vinylnaphthalene" refers to a molecule containing a naphthalene aromatic system, a vinyl group bonded to an aromatic carbon atom of that naphthalene aromatic system, and one or more substituents bonded to the aromatic carbon atom of that naphthalene aromatic system. In other words, the molecular structure of the substituted 1-vinylnaphthalene contains at least two substituents bonded to the aromatic carbon atom of that naphthalene aromatic system, one of which is a vinyl group bonded to the carbon atom at position 1 of the naphthalene aromatic system (see Formula 1). In other words, "substituted 1-vinylnaphthalene" has one or more substituents in addition to the vinyl substituent on the aromatic carbon atom of the naphthalene aromatic system. These one or more substituents cannot be hydrogen.

[0048] The term "substituted 2-vinylnaphthalene" refers to a vinyl group containing a naphthalene aromatic system and aromatic carbon atoms bonded to that naphthalene aromatic system. [and] a molecule with one or more substituents, wherein the one or more substituents are bonded to the aromatic carbon atom of the naphthalene aromatic system. That is, the molecular structure of the substituted 2-vinylnaphthalene contains at least two substituents bonded to the aromatic carbon atom of the naphthalene aromatic system, one of which is a vinyl group bonded to the carbon atom at position 2 of the naphthalene aromatic system (see Formula 1). In other words, "substituted 2-vinylnaphthalene" has one or more substituents on the aromatic carbon atom of the naphthalene aromatic system in addition to the vinyl substituent. These one or more substituents cannot be hydrogen. Formula I Formula 2

[0049] For the purposes of this invention, the numbering of the substituents in the vinyl naphthalene may not strictly follow the IUPAC rules. For the purposes of this invention, 1-vinyl naphthalene is any naphthalene having a vinyl group covalently bonded to an aromatic carbon of the naphthalene aromatic system, wherein the aromatic carbon is adjacent to carbon 4a or carbon 8a of the naphthalene. For the purposes of this invention, 2-vinyl naphthalene is any naphthalene having a vinyl group covalently bonded to an aromatic carbon of the naphthalene aromatic system, wherein the aromatic carbon is neither adjacent to carbon 4a nor carbon 8a of the naphthalene aromatic system. For the purposes of this invention, this means that the numbering of the vinyl group takes precedence over any other group covalently bonded to the aromatic carbon of the naphthalene aromatic system. That is, 2-chloro-6-naphthalene (shown in Formula 3) is still considered 2-vinyl naphthalene because the vinyl group in this compound is covalently bonded to an aromatic carbon of the naphthalene aromatic system, wherein the aromatic carbon is neither adjacent to carbon 4a nor carbon 8a of the naphthalene. The aromatic carbons of the naphthalene aromatic system are carbons 1, 2, 3, 4, 4a, 5, 6, 7, 8, and 8a. In other words, the compound "2-chloro-6-vinylnaphthalene" is considered 2-vinylnaphthalene because it is equivalent to the less "formally acceptable" name "2-vinyl-6-chloronaphthalene". Formula 3

[0050] The term "macromonomer" (or "giant monomer") is used to describe a relatively high molecular weight species (above 500 g / mol) possessing a single functional group that can participate in polymerization. In other words, although the macromonomer has a high molecular weight or internal monomer unit in its molecular structure, it can function as a monomer. Therefore, a macromonomer can be considered a polymer. Typically, a macromonomer contributes a single monomer unit to the resulting polymer.

[0051] For the purposes of this application, the term "copolymer" refers to a polymer containing two or more different repeating units. A macromonomer is considered to contain multiple repeating units. Copolymers can be formed from two or more monomers of different types. For example, for the purposes of this invention, a ternary copolymer is considered a copolymer. That is, copolymers can be formed from two, three, four, or other different types of monomers.

[0052] Examples of electro-optic devices include electro-optic material layers comprising an electrophoretic medium encapsulated in microcapsules or microcells, as described in U.S. Patent No. 6,982,178. Figure 1 shows a side view of an example of the structure of a portion of an electro-optic device comprising microcapsules. The electro-optic device 100 includes: a first electrode layer 101 comprising light-transmitting electrodes, an electro-optic material layer 102, a first adhesive layer 104, and a second electrode layer 103, the second electrode layer comprising a plurality of pixel electrodes. The first adhesive layer 104 connects the electro-optic material layer 102 and the second electrode layer 103. The electro-optic material layer 102 comprises a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and includes an electrophoretic medium 122 having particles in a nonpolar liquid. Typically, the plurality of microcapsules are retained within a polymeric adhesive 132. A viewer can view an image of the device 100 from a viewing side 150. The electro-optic device 100 may be constructed from a front plane laminate, as described in the background of the invention.

[0053] Another example of an electro-optic device is shown in Figure 2. Figure 2 illustrates a side view of an example of the basic structure of a portion of an electro-optic device having microcapsules. The electro-optic device 200 has a viewing side 150. It sequentially includes: a first electrode layer 101 containing light-transmitting electrodes, a second adhesive layer 105, an electro-optic material layer 102, a first adhesive layer 104, and a second electrode layer 103 containing a plurality of pixel electrodes. The second adhesive layer 105 connects the first electrode layer 101 to the electro-optic material layer 102. The first adhesive layer 104 connects the electro-optic material layer 102 to the second electrode layer. The electro-optic material layer 102 contains a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and includes an electrophoretic medium 122 containing particles in a nonpolar liquid. Typically, the plurality of microcapsules are retained within a polymer adhesive 132. The electro-optic device 200 can be constructed from a dual release liner as described above.

[0054] The microcapsule electro-optic devices of Figures 1 and 2 may further include a light-transmitting front substrate (not shown in Figures 1 and 2) adjacent to the first electrode layer 101, wherein the electrode layer is disposed between the front substrate and the electro-optic material layer (for the device of Figure 1) or between the front substrate and the second adhesive layer (for the device of Figure 1). The front substrate may be a plastic film, such as a polyethylene terephthalate (PET) sheet having a thickness of 25 to 200 µm. The front substrate may further include one or more additional layers, such as a protective layer for absorbing ultraviolet radiation, a barrier layer for preventing oxygen or moisture from entering the device, and an anti-reflective coating for improving the optical properties of the device.

[0055] An example of an electro-optic device comprising microcells is illustrated in Figure 3. The electro-optic device 300 of Figure 3 sequentially comprises: a first electrode layer 101, an electro-optic material layer 202, an adhesive layer 204, and a second electrode layer 103 comprising a plurality of pixel electrodes. The adhesive layer 204 connects the sealing layer 232 of the electro-optic material layer 202 to the second electrode layer 103. The electro-optic material layer 202 of the electro-optic device 300 comprises a plurality of microcells 212 and a sealing layer 232. Each microcell 212 has a bottom 242, a partition wall 252, and an opening, and the sealing layer 232 spans the opening of each microcell. Each microcell 212 comprises an electrophoretic medium 122. The electrophoretic medium 122 contains a plurality of first-type particles 272 and a plurality of second-type particles 262 in a non-polar liquid. A viewer can view an image of the device 300 from a viewing side 250.

[0056] The micro-cell electro-optic device of Figure 3 may further include a light-transmitting front substrate (not shown in Figure 3) adjacent to the first electrode layer 101, wherein the electrode layer is disposed between the front substrate and the electro-optic material layer. The light-transmitting front substrate may be a plastic film, such as a polyethylene (PET) sheet having a thickness of 25 to 200 µm. The light-transmitting front substrate may further include one or more additional layers, such as a protective layer for absorbing ultraviolet radiation, a barrier layer for preventing oxygen or moisture from entering the device, and an anti-reflective coating for improving the optical properties of the device.

[0057] In the electro-optic devices of Figures 1, 2 and 3, the first electrode layer may be a conductive layer with a thin, continuous coating of conductive material that has minimal intrinsic electromagnetic radiation absorption in the visible spectrum, such as indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), graphene or similar materials.

[0058] The electrophoretic medium 122 of the electro-optic device illustrated in Figures 1, 2, and 3 comprises a plurality of first-type pigment particles and a plurality of second-type pigment particles. Each of the plurality of first-type particles comprises a core and a shell, the core comprising an organic pigment. Each of the plurality of second-type particles may also comprise an organic pigment. The electrophoretic medium 122 may further comprise a plurality of third-type particles and a plurality of fourth-type particles. The electrophoretic medium 122 may further comprise a plurality of fifth-type particles. That is, the electrophoretic medium 122 may comprise a plurality of first, second, third, and fourth-type particles. The second-type particles may also comprise organic pigments. The content of electrophoretic particles in the nonpolar liquid can vary. For example, one type of particle may account for 0.1% to 50%, preferably 0.5% to 15%, based on the volume of the nonpolar liquid.

[0059] The electrophoretic medium of the present invention may contain a charge control agent (CCA). The CCA controls the charge on the electrophoretic particles. The CCA is a surfactant-like molecule having ionic or other polar groups, hereinafter referred to as head groups; and a nonpolar chain (typically a hydrocarbon chain), hereinafter referred to as tail. The CCA can recombine with or adsorb onto the charged particles. It is believed that the CCA forms invert cells in the electrophoretic medium. These are small groups of charged invert cells that contribute to conductivity in the medium. These invert cells contain a polar core, the size of which can vary from 1 nm to tens of nanometers, and can have spherical, cylindrical, or other geometric shapes surrounded by the nonpolar tail groups of the CCA molecule. Typically, three phases can be distinguished in the electrophoretic medium: solid particles with surfaces, a highly polar phase (invert cells) distributed in the form of tiny droplets, and a continuous phase containing the nonpolar fluid. Both the electrophoretic particles and the charged invert cells can move through the fluid after an electric field is applied. Therefore, there are two parallel pathways for electrical conduction via the fluid (which typically has imperceptibly low conductivity). The charge control agent in the electrophoretic medium can be 0.1 to 8 wt%, 0.3 to 7 wt%, 0.5 to 5 wt%, 0.6 to 4 wt%, 0.7 to 3 wt%, or 0.8 to 2 wt% of the charge control agent, based on the weight of the electrophoretic medium.

[0060] The electrophoretic medium of the present invention comprises particles suspended in a nonpolar liquid. The nonpolar liquid may be transparent and colorless. Preferably, it has a dielectric constant in the range of about 2 to about 30, more preferably about 2 to about 15, for high particle mobility. Examples of suitable dielectric solvents include hydrocarbons such as isoparaffins, decaline, 5-ethylidene-2-norbornene, fatty oils, and 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) from TCI America, Portland, Oregon; and poly(chlorotrifluoroethylene), such as Halocarbon from Halocarbon Product Corp., River Edge, NJ. Oils; perfluoropolyalkyl ethers, such as Galden from Ausimont or Krytox Oils and Greases K-Fluid series from DuPont, Delaware; polydimethylsiloxane polysiloxane oil (DC-200) from Dow-corning.

[0061] Microcells can be formed in batch processes or in a continuous roll-to-roll process, as disclosed in U.S. Patent No. 6,933,098. The latter provides a continuous, low-cost, high-volume manufacturing technique for producing compartments used in a variety of applications, including electro-optic devices. Microcell arrays suitable for use in this invention can be produced using microimprinting, as illustrated in Figure 4. A male mold 402 can be placed on a web 404, as shown in Figure 4; or under the web 404 (not shown); however, alternative arrangements are possible. See U.S. Patent No. 7,715,088, the entire contents of which are incorporated herein by reference. A conductive substrate can be constructed by forming a conductive film 401 (first electrode) on a polymer substrate, wherein the polymer substrate will become a support for a device. A composition 400 comprising a thermoplastic, thermosetting, or precursor thereof is then coated onto the conductive film. The thermoplastic or thermosetting precursor layer is imprinted using a mold in the form of a roller, plate, or conveyor belt at a temperature higher than the glass transition temperature of the thermoplastic or thermosetting precursor layer.

[0062] The thermoplastic or thermosetting precursors used for the preparation of microcells can be multifunctional acrylates or methacrylates, vinyl ethers, epoxides and their oligomers or polymers, and the like. Combinations of multifunctional epoxides and multifunctional acrylates are also very useful for achieving the desired physical-mechanical properties. Crosslinkable oligomers such as urethane acrylates or polyester acrylates can be added to impart flexibility and improve the flexural resistance of the imprinted microcells. The composition may contain polymers, oligomers, monomers, and additives, or only oligomers, monomers, and additives. The glass transition temperature (or Tg) of this type of material is typically in the range of about -70 °C to about 150 °C, preferably about -20 °C to about 50 °C. The microimprinting method is typically carried out at temperatures above this Tg. The microimprinting temperature and pressure can be controlled using a heated die or a heated housing substrate (to which the die applies pressure).

[0063] As shown in Figure 4, the mold is released during or after the curing of the precursor layer to expose the array of microcells 403. Curing of the precursor layer can be achieved by cooling, solvent evaporation, or crosslinking by radiation, heat, or moisture. If the curing of the thermosetting precursor is achieved by UV radiation, UV light can irradiate the transparent conductor film from the bottom or top of the mesh. Alternatively, the UV lamp can be placed inside the mold. In this case, the mold must be transparent to allow UV light to pass through the pre-patterned mold and irradiate the thermosetting precursor layer. The mold can be prepared by any suitable method, such as diamond turning or photoresist methods, followed by etching or electroplating. The master template for the mold can be manufactured by any suitable method, such as electroplating. In the case of electroplating, a thin layer of a sub-metal such as chromium-nickel alloy (typically 3000 Å) is sputtered onto a glass substrate. Then, a photoresist layer is applied to the mold and it is exposed to UV light. A mask is placed between the UV and the photoresist layer. The exposed areas of the photoresist harden. The unexposed areas are then removed by cleaning with a suitable solvent. The remaining hardened photoresist is dried and a thin layer of a sub-metal is sputtered again. The master template is then ready for electroforming. A typical material used for electroforming is nickel-cobalt. Alternatively, the master template can be made of nickel by electroforming or electroless nickel deposition. The bottom layer of the template is typically between approximately 50 and 400 µm. The master template can also be made using other microengineering techniques, including electron beam writing, dry etching, chemical etching, laser writing, or laser interference, as described in "Replication techniques for micro-optics", SPIE Proc. Vol. 3099, pp.76-82 (1997). Alternatively, the template can be made using photomachining, using plastics, ceramics, or metals.

[0064] Before applying the UV-curable resin composition, the mold may be treated with a release agent to aid in the demolding process. The UV-curable resin may be degassed prior to dispensing and may selectively contain a solvent. This solvent, if present, readily evaporates. The UV-curable resin is dispensed onto the mold by any suitable method such as coating, impregnation, or pouring. The dispenser may be mobile or stationary. A conductive film covers the UV-curable resin. If necessary, pressure may be applied to ensure proper adhesion between the resin and the plastic and to control the thickness of the underlying layer of the microcells. This pressure may be applied using laminating rollers, vacuum molding, pressurizing devices, or any other similar means. If the mold is metallic and opaque, the plastic substrate is typically transparent to the photochemical radiation used to cure the resin. Conversely, the mold may be transparent, and the plastic substrate may be opaque to this photochemical radiation. In order for the molded configuration to transfer well onto the transfer film, the conductor film needs to have good adhesion to the UV-curable resin, and the resin should have good release properties to the mold surface.

[0065] Photolithography. Photolithography can also be used to fabricate microcells. The photolithography process used to fabricate microcell arrays is illustrated in Figures 5A and 5B. As shown in Figures 5A and 5B, the microcell array 500 can be fabricated by exposing a radiation-curable material 501a coated onto a conductor film 502 by a known method to UV light (or alternatively, other forms of radiation, electron beams, and the like) through a mask 506 to form partition walls 501b corresponding to the image projected through the mask 506. The substrate conductor film 502 is preferably mounted on a support substrate mesh 503 that may contain plastic material.

[0066] In the photomask 506 of Figure 5A, the dark squares 504 represent the opaque areas, and the spaces between the dark squares represent the transparent areas 505 of the photomask 506. The UV irradiation reaches the radiation-curable material 502a via the transparent areas 505. Preferably, the exposure is performed directly on the radiation-curable material 502a, i.e., the UV radiation does not pass through the substrate 503 or the substrate conductor 502 (top exposure). For this reason, neither the substrate 503 nor the conductor 502 needs to be transparent to UV or other radiation wavelengths used.

[0067] As shown in Figure 5B, the exposed area 501b hardens, and then the unexposed area (protected by the opaque area 504 of the mask 506) is removed by a suitable solvent or developer to form microcells 507. The solvent or developer is selected from those commonly used to dissolve or reduce the viscosity of the radiation-curable material, such as methyl ethyl ketone (MEK), toluene, acetone, isopropanol, or the like. Similarly, the preparation of these microcells can be achieved by placing a photomask under the conductor film / substrate support mesh, in which case the UV light is irradiated from the bottom via the photomask, and the substrate needs to be radiation-transparent.

[0068] Imaging Exposure. Another alternative method for preparing the microcell array of the present invention by imaging exposure is illustrated in Figures 5C and 5D. When using opaque conductor lines, these conductor lines can be used as a photomask for bottom exposure. Additional exposure from the top through a second photomask having opaque lines perpendicular to the conductor lines forms durable microcell partitions. Figure 5C illustrates the fabrication of the microcell array 510 of the present invention using both top and bottom exposure principles. The substrate conductor film 512 is opaque and patterned with lines. The radiation-curable material 511a coated on the substrate conductor 512 and substrate 513 is exposed from the bottom through the conductor line pattern 512, which serves as the first photomask. A second exposure is performed from the "top" side through a second photomask 516 having a line pattern perpendicular to the conductor lines 512. The spaces 515 between these lines 514 are substantially transparent to UV light. In this process, the partition wall material 511b is cured from bottom to top in a transverse orientation and from top to bottom in a vertical orientation, thereby forming complete microcells 517. As shown in Figure 5D, the unexposed areas are then removed by a solvent or developer as described above to expose the microcells 517.

[0069] These microcells can be constructed from thermoplastic elastomers that have good compatibility with them and do not interact with the electrophoretic medium. Examples of useful thermoplastic elastomers include diblock, triblock, and multiblock copolymers of the ABA and (AB)n types, wherein A is styrene, α-methylstyrene, ethylene, propylene, or norbornene; B is butadiene, isoprene, ethylene, propylene, butene, dimethylsiloxane, or propylene sulfide; and A and B in the formula cannot be the same. The number n is ≥1, preferably 1-10. Diblock or triblock copolymers of styrene or ox-methylstyrene are particularly useful, such as SB (poly(styrene-b-butadiene)), SBS (poly(styrene-b-butadiene-b-styrene)), SIS (poly(styrene-b-isoprene-b-styrene)), SEBS (poly(styrene-b-ethylene / butene-b-styrene)), poly(styrene-b-dimethylsiloxane-b-styrene), poly((α-methylstyrene-b-isoprene), poly(α-methylstyrene-b-isoprene-b-α-methylstyrene), poly(α-methylstyrene-b-propenesulfide-b-α-methylstyrene), and poly(α-methylstyrene-b-dimethylsiloxane-b-α-methylstyrene). Commercially available styrene block copolymers are particularly useful, such as the Kraton D and G series (from Kraton). Polymer, Houston, Tex. Crystalline rubbers, such as poly(ethylene-co-propylene-co-5-methylene-2-norbornene); or EPDM (ethylene-propylene-diene terpolymer) rubbers, such as Vistalon 6505 (from Exxon Mobil, Houston, Tex.) and its graft copolymers, have also been found to be particularly useful.

[0070] The thermoplastic elastomer is soluble in a solvent or solvent mixture, wherein the solvent is immiscible with the display fluid in the microcell and has a lower specific gravity than the display fluid. For the overcoating composition, a low surface tension solvent is preferred because it has better wetting properties on the microcell septa and the electrophoretic fluid. A solvent or solvent mixture with a surface tension below 35 dynes / cm is preferred. A surface tension below 30 dynes / cm is even more preferred. Suitable solvents include alkanes (preferably C6-12 alkanes, such as heptane, octane, or Isopar solvent from Exxon Chemicals, nonane, decane, and their isomers), cycloalkanes (preferably C6-12 cycloalkanes, such as cyclohexane and naphthane, and their analogs), alkylbenzenes (preferably mono- or di-C1-6 alkylbenzenes, such as toluene, xylene, and their analogs), alkyl esters (preferably C2-5 alkyl esters, such as ethyl acetate, isobutyl acetate, and their analogs), and C3-5 alkyl alcohols (such as isopropanol, their analogs, and their isomers). Mixtures of alkylbenzenes and alkanes are particularly useful.

[0071] In addition to polymer additives, the polymer mixture may also include wetting agents (surfactants). Wetting agents (such as FC surfactants from 3M, Zonyl fluorinated surfactants from DuPont, fluoroacrylates, fluoromethyl acrylates, fluorinated long-chain alcohols, perfluorinated long-chain carboxylic acids and their derivatives, and Silwet polysiloxane surfactants from OSi, Greenwich, Conn.) may also be included in the composition to improve the adhesion of the sealant to the microcells and provide a more flexible coating method. Other components, including crosslinking agents (e.g., diazides, such as 4,4'-diazidodiphenylmethane and 2,6-di-(4'-azidobenzyl)-4-methylcyclohexanone), vulcanizing agents (e.g., 2-benzothiazole disulfide and tetramethylthiuram disulfide), multifunctional monomers or oligomers (e.g., hexanediol, diacrylate, trimethylolpropane, triacrylate, divinylbenzene, diallylphthalene), thermal initiators (e.g., dilauryl peroxide, benzyl peroxide), and photoinitiators (e.g., isopropyl thioxanthone (ITX), Irgacure 651 and Irgacure 369 from Ciba-Geigy), are also highly useful for improving the physical-mechanical properties of the sealant through crosslinking or polymerization reactions during or after the external coating process.

[0072] After fabrication of these microcells, they are filled with a suitable electrophoretic medium. The microcell array 640 can be prepared by any of the methods described above. As shown in cross-section in Figures 6A-6D, the microcell partition walls 661 extend upward from the substrate 663 to form the open cell. The microcells may include an undercoat 662 to passivate the mixture and prevent the microcell material from interacting with the mixture containing the electrophoretic medium 665.

[0073] Next, the microcells are filled with an electrophoretic medium 664 containing particles 665 in a nonpolar fluid. These microcells can be filled using various techniques. In some embodiments, a doctor blade coating method can be used to fill the microcells to the depth of the microcell septa 661. In other embodiments, inkjet microinjection can be used to fill the microcells. In still other embodiments, a microneedle array can be used to fill the microcell array.

[0074] As shown in Figure 6C, after filling, the microcells are sealed by applying polymer 1466, which forms the sealing layer. In some embodiments, the sealing method may include exposure to hot, dry air or UV radiation. The polymer 666 is compatible with the electrophoretic medium but is not fluidized by the electrophoretic medium 664. Therefore, the final microcell structure is largely unaffected by leakage and can withstand flexural deformation without delamination.

[0075] Iterative photolithography can be used to fill a variety of individual microcells with a desired electrophoretic medium. This method typically involves coating an array of empty microcells with a positively reactive photoresist layer; exposing the photoresist by imaging; selectively opening a number of microcells by developing the photoresist; filling the opened microcells with a desired mixture; and sealing the filled microcells by a sealing method.

[0076] After filling the microcells 660, a trimming layer 668 can be laminated onto the sealed array, preferably by pre-coating the trimming layer 668 with an adhesive layer, wherein the adhesive layer may be a pressure-sensitive adhesive, a hot-melt adhesive, or a heat, moisture, or radiation-curable adhesive. If the top conductor film is transparent to radiation, the laminated adhesive can be post-cured by radiation such as UV passing through the top conductor film.

[0077] This invention provides an electrophoretic medium comprising a nonpolar liquid, a plurality of first-type particles, and a plurality of second-type particles. Each of the plurality of first-type particles has a core and a shell. The core may contain an organic pigment. The shell contains a polymer that is in contact with the surface of the pigment in the core. The polymer in the shell may be a homopolymer or a copolymer. The homopolymer may be formed from vinylnaphthalene. The copolymer may be formed from vinylnaphthalene and a first monomer. The homopolymer or copolymer is in contact with the surface of the organic pigment in the core. The core-shell first-type particles may be formed by dispersion polymerization. In one embodiment, the dispersion polymerization is a free radical polymerization of the monomer or a plurality of monomers in the presence of the pigment particles. When the core-shell particles are obtained by dispersion polymerization, the polymer in the shell is adsorbed onto the surface of the pigment in the core.

[0078] The vinylnaphthalene may be 1-naphthalene, 2-naphthalene, 1-naphthalene having one or more substituents on the aromatic carbon of the vinylnaphthalene, or 2-naphthalene having one or more substituents on the aromatic carbon of the vinylnaphthalene.

[0079] The vinylnaphthalene may have halogen substituents. Non-limiting examples of halogen-substituted 1-naphthalene and 2-naphthalene include 6-chloro-2-vinylnaphthalene, 6-bromo-2-vinylnaphthalene, 6-fluoro-2-vinylnaphthalene, 4-chloro-1-vinylnaphthalene, 4-bromo-1-vinylnaphthalene, 4-fluoro-1-vinylnaphthalene, 1-chloro-2-vinylnaphthalene, 1-bromo-2-vinylnaphthalene, and 1-fluoro-2-vinylnaphthalene.

[0080] The vinylnaphthalene may have an alkoxy substituent. The alkoxy substituent may be a methoxy or ethoxy substituent. Non-limiting examples of alkoxy-substituted 1-naphthalene and 2-naphthalene include 6-methoxy-2-vinylnaphthalene, 7-methoxy-1-vinylnaphthalene, 4-methoxy-1-vinylnaphthalene, and 4-methoxy-2-vinylnaphthalene.

[0081] The vinylnaphthalene may have an alkyl substituent. The alkyl substituent may be methyl, ethyl, propyl, butyl, pentyl or other alkyl groups. Non-limiting examples of alkyl-substituted 1-naphthalene and 2-naphthalene include 1-methyl-2-vinylnaphthalene and 4-methyl-2-vinylnaphthalene.

[0082] Other non-limiting examples of substituted 1-vinylnaphthalene and 2-vinylnaphthalene include 2-nitro-1-vinylnaphthalene, 6-carboxylic acid methyl ester-2-vinylnaphthalene, 6-hydroxy-2-vinylnaphthalene, 1-(2-fluorophenyl)-2-vinylnaphthalene and 2,7-bis(vinyl)naphthalene.

[0083] The shell of the first type of particle may contain a copolymer. The copolymer may be formed by reacting vinylnaphthalene with a first monomer. The first monomer may be a macromolecular monomer.

[0084] Non-limiting examples of the first monomer include styrene, α-methylstyrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tributyl acrylate, tributyl 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, n-octyl methacrylate, propylene. Octadecyl methacrylate, 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 or their analogues.

[0085] The macromonomer may include terminal functional groups selected from the group consisting of: acrylate, methacrylate, vinyl, or combinations thereof.

[0086] Examples of macromonomers that can be used to form the first type of particle are described in U.S. Patent Application No. 2018 / 0210312, the entire contents of which are incorporated herein by reference. One type of macromonomer that can be used to form the shell of the core-shell particle includes acrylate-terminated polysiloxanes, such as, for example, Gelest's MCR-M11, MCR-M17, or MCR-M22. The macromonomer may have a molecular structure comprising (i) polydimethylsiloxane and (ii) vinyl functional groups, methacrylate groups, or acrylate groups.

[0087] Another type of macromolecular monomer system suitable for this process, PE-PEO macromolecular monomer, is shown below: RmO-[-CH2CH2O-]n-CH2-phenyl-CH=CH2; or RmO-[-CH2CH2O-]nC(=O)-C(CH3)=CH2. The substituent R can be a polyethylene chain, with n-series chains ranging from 1 to 60 and m-series chains from 1 to 500. Synthetic methods for these compounds can be found in Dongri Chao et al., *Polymer Journal*, Vol. 23, no. 9, 1045 (1991); and Koichi Ito et al., *Macromolecules*, 1991, 24, 2348. Another suitable type of macromolecular monomer system for PE macromonomers is shown below: CH3-[-CH2-]n-CH2O-C(=O)-C(CH3)=CH2. In this case, n is 30-100. The synthesis of this type of macromolecular monomer can be found in Seigou Kawaguchi et al., Designed Monomers and Polymers, 2000, 3, 263.

[0088] The first monomer may be selected from the group consisting of: methyl methacrylate, lauryl methacrylate, 2,2,2-trifluoroethyl methacrylate, acrylate-terminated polysiloxanes, and methacrylate-terminated polysiloxanes.

[0089] The copolymer may be formed from vinylnaphthalene, a first monomer, and a second monomer. The copolymer may be formed from: vinylnaphthalene, 2,2,2-trifluoroethyl methacrylate, and a macromonomer having a structure including (i) polydimethylsiloxane and (ii) vinyl, acrylate, or methacrylate functional groups. The macromonomer may be a monomethacryloxypropyl-terminated polydimethylsiloxane. The second monomer may be selected from examples of the monomers described above for the first monomer (including the macromonomer).

[0090] The copolymer may be formed from vinylnaphthalene, a first monomer, a second monomer, and a third monomer. The third monomer may be selected from examples of the monomers described above for the first monomer (including macromonomers).

[0091] The electrophoretic medium contains a first type of particle and a second type of particle, wherein the first type of particle has an opposite charge polarity to the second type of particle.

[0092] The electrophoretic medium may contain type I particles, type II particles, type III particles, and type IV particles. The type I, II, III, and IV particles may have different colors; the type I, II, III, and IV particles may contain organic pigments. The type I, II, and III particles may have an electric charge polarity opposite to that of the type IV particles. The type IV particles may contain inorganic pigments. The colors of the type I, II, and III pigments may be selected from the group consisting of: blue, red, yellow, cyan, magenta, and green. The color of the type IV pigment may be white.

[0093] In one embodiment, the first, second, and third types of particles can be selected from a group consisting of blue, red, and yellow; and the fourth type of particle can be white. In this embodiment, the first type of particle can be yellow.

[0094] In another embodiment, the first, second, and third type particles can be selected from the group consisting of cyan, magenta, and yellow; and the fourth type particle can be white. In this embodiment, the first type particle can be magenta.

[0095] The electrophoretic medium may contain type I particles, type II particles, type III particles, and type IV particles. The type I, II, III, and IV particles may have different colors; the type I, II, and III particles may contain organic pigments. The type I and II particles may have an opposite charge polarity to the type III and IV particles. The type IV particles may contain inorganic pigments. The colors of the type I, II, and III pigments may be selected from the group consisting of: blue, red, yellow, cyan, magenta, and green. The color of the type IV pigment may be white.

[0096] The electrophoretic medium may comprise first-type particles, second-type particles, third-type particles, fourth-type particles, and fifth-type particles. The first, second, third, fourth, and fifth-type particles have different colors; the first, second, and third-type particles may contain organic pigments. The first and second-type particles may have a charge polarity opposite to that of the third and fourth-type particles. The fourth-type particles may contain inorganic pigments. The colors of the first, second, and third-type pigments may be selected from the group consisting of cyan, magenta, and yellow. The color of the fourth-type pigment may be white. The first and fourth-type particles may carry a negative charge, while the second, third, and fifth-type particles may carry a positive charge. The first-type particles may have a more negative zeta potential than the fourth-type particles. The fifth-type particles may have a greater zeta potential than the second and third-type particles. The colors of the fourth and fifth-type particles may be selected from the group consisting of white and black. In one embodiment, the electrophoretic medium of the present invention comprises first, second, third, fourth, and fifth-type particles, each having a color of yellow, red, blue, white, and black. In this embodiment, the first and fourth type particles are negatively charged, and the zeta potential of the first type particle is more negative than that of the fourth type particle. In the same embodiment, the second, third, and fifth type particles are positively charged, and the fifth type particle has a zeta potential greater than that of the second and third type particles.

[0097] The organic pigment of the nucleus of the first type of particle can be selected from the group consisting of: azo pigments, phthalocyanine pigments, quinacrine 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.

[0098] The organic pigments of the first, second, and third types of particles can each be independently selected from the following groups: 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, 28 2 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.

[0099] The electrophoretic medium of the present invention can be manufactured by a method comprising the following steps: (a) providing a dispersion of an organic pigment in a first organic solvent; (b) adding vinylnaphthalene, a first monomer, and a free radical initiator to the dispersion and mixing to form the first type of particles; (c) washing the first type of particles with a second organic solvent; (d) removing the first and second organic solvents; and (e) dispersing the washed particles in a nonpolar liquid. The method may further comprise a step of adding a charge control agent to the dispersion of the washed particles in the nonpolar liquid.

[0100] The organic pigments of the first type of particle core of the present invention may have an average diameter of 10 nm to about 100 µm, 50 nm to 1 µm, or 100 nm to 800 nm.

[0101] Organic pigments provide color because they absorb specific wavelengths of incident light that correspond to visible light. Typically, their color saturation and intensity increase as particle size decreases (that is, as surface area increases). Therefore, most of them can be obtained as particles with a fairly high surface area, making them quite difficult to disperse and stabilize in liquids.

[0102] The electrophoretic medium of the present invention may comprise a plurality of first, second, third, and fourth type particles. The first type particle comprises a core and a shell. The core comprises an organic pigment and the shell comprises a polymer. The second type particle may also comprise a core and a shell, wherein the core comprises an organic pigment and the shell comprises a polymer. The third type particle may also comprise a core and a shell, wherein the core comprises an organic pigment and the shell comprises a polymer. The fourth type particle may also comprise a core and a shell, wherein the core comprises an inorganic pigment and the shell comprises a polymer.

[0103] For the manufacture of type I particles, the amounts of the reagents used (e.g., organic pigments, vinyl naphthalene, a first monomer, a second monomer, if present, a third monomer, if present, and an initiator) can be adjusted to achieve the desired core-shell particle content. The manufacturing method may include more than one stage and / or more than one polymerization type.

[0104] First-type particles, manufactured according to various specific embodiments of the invention, are dispersed in a nonpolar liquid. Ideally, the polymer layer is compatible with the nonpolar liquid. In practice, the nonpolar liquid suspended in the electrophoretic medium is typically hydrocarbon-based; however, the nonpolar liquid may include a proportion of halogenated carbons, used to increase the density of the nonpolar liquid and thus reduce the density difference between the nonpolar liquid and the particles. Therefore, the polymer of the shell may include hydrocarbon chains to achieve compatibility with the nonpolar liquid of the electrophoretic medium, thereby improving the dispersion stability of the particles. In one embodiment of the first-type particles, the polymer of the shell may have a branched or "comb" structure, having a main chain and a plurality of side chains extending from the main chain. Each of these side chains may have four, five, six, or more carbon atoms. These side chains themselves may be branched; for example, each side chain may be a branched alkyl group, such as 2-ethylhexyl.

[0105] There are two basic methods for forming this comb polymer. The first method uses monomers that inherently provide the desired side chains. Typically, this monomer has a single polymerizable group at one end of a long chain (at least four, and preferably at least six carbon atoms). Monomers of this type have been found to provide good results in this method, including 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 is desirable to limit the number of side chains formed in these methods, and this can be achieved by using a mixture of monomers (e.g., a mixture of lauryl methacrylate and methyl methacrylate) to form a random copolymer in which only certain repeating units carry long side chains. In the second method, represented by the RGP-ATRP method, a first polymerization reaction is carried out using a mixture of monomers, at least one of which carries a starting group, thus producing a first polymer including this starting group. Then, the product of this first polymerization reaction is subjected to a second polymerization, typically under different conditions than the first polymerization, so as to cause the starting groups in the polymer to cause additional monomer polymerization on the original polymer, thus forming the desired side chains.

[0106] Free radical polymerization of ethylene or similar free radical polymerizable groups attached to particles can be carried out at elevated reaction temperatures, preferably 60 to 70 °C, using known free radical initiators such as azobis(isobutyronitrile) (AIBN). Meanwhile, ATRP polymerization can be carried out using known metal complexes, as described in Wang, JS et al., Macromolecules 1995, 23, 7901 and J. Am. Chem. Soc. 1995, 117, 5614, and in Beers, K. et al., Macromolecules 1999, 32, 5772-5776. See also U.S. Patent Nos. 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, a preferred catalyst for ATRP is cuprous chloride in the presence of bispyridyl (Bpy) groups.

[0107] An optimal range has been identified for the amount of polymer layer that should form on electrophoretic particles, and an excessive amount of polymer on these particles can reduce their electrophoretic characteristics. This optimal range will vary with several factors, including the density and size of the particles to be coated, the nature of the suspending medium in which the particles are intended to be used, the nature of the polymer in the particle shell, and, for any given particle, the polymer and nonpolar liquid nature of the electrophoretic medium; this optimal range is preferably determined empirically. However, as a general guideline, it should be noted that the denser the particles, the lower the optimal polymer content by weight; and the more finely separated the particles, the higher the optimal polymer content. Typically, the polymer content of the particles can be higher than 2%, 4%, or 6% by weight, by weight.

[0108] The polymer content of the particles can be 1 to 50 percent by weight, 2 to 30 percent by weight, 4 to 20 percent by weight, 5 to 15 percent by weight, 4 to 15 percent by weight, 6 to 15 percent by weight, or 8 to 12 percent by weight, based on the weight of the particles.

[0109] Example

[0110] Example 1: Preparation of Creative Yellow Particles

[0111] In a 500 mL bottle, 60.0 g of Pigment Yellow 138 (Paliotol Yellow L 0962 HD supplied by BASF) was mixed with 88.8 g of monomethacryloxypropyl-terminated polydimethylsiloxane (MCR-M22 supplied by Gelest) and 480 mL of trimethylsiloxy-terminated polydimethylsiloxane (DMS-T01 supplied by Gelest). The mixture was stirred for 30 minutes. The resulting mixture was transferred to a 1 L reactor and 6.7 g of 2,2,2-trifluoroethyl methacrylate (supplied by Sigma) was added. The temperature was increased to 75 °C with stirring and under nitrogen. When the temperature reached 75 °C, a solution of 10.0 g of 2-vinylnaphthalene (supplied by Sigma) in 4 g of ethyl acetate (supplied by Sigma) was added to the mixture. After 1 hour under nitrogen purging, a solution of 0.304 g of lauryl peroxide initiator (supplied by Sigma) dissolved in 3.5 g of ethyl acetate (supplied by Sigma) was added to the reactor to initiate the polymerization. After 19 hours, the mixture was centrifuged at 5000 rpm for 20 minutes and the supernatant was removed. The resulting solids were redispersed in Isopar E, the dispersion was centrifuged, and the supernatant was removed. This washing cycle was repeated twice, and the solids were dried under vacuum at room temperature to produce the particles. The final pigment had a polymer content of 11%; the zeta potential of the particles was -51 mV.

[0112] Example 2: Preparation and color evaluation of an innovative electro-optic device.

[0113] An electrophoretic medium was prepared using a charge control agent, a hydrocarbon solvent, and negatively charged yellow particles, positively charged blue particles, positively charged red particles, and negatively charged white particles from Example 1. A microcellular electro-optic device was fabricated using this electro-optic medium. The device was driven to white, dark, red, yellow, blue, and green states. The color of each state was measured using a colorimeter. Table 1 shows the color measurement results (in L*a*b*) for Example 2. W represents white, K represents black, R represents red, Y represents yellow, B represents blue, and G represents green.

[0114] Comparative Example 3: Preparation and color evaluation of the control electro-optic device.

[0115] The procedure of Example 2 was repeated, but for the comparative electrophoresis medium, control yellow particles were used instead of the yellow particles from Example 1. The control yellow particles comprised a core and a shell, the core containing the same pigment yellow 138 as used in Example 1, and the shell being formed by the polymerization of methyl methacrylate, monomethacryloxypropyl-terminated polydimethylsiloxane, and 2,2,2-trifluoroethyl methacrylate. Table 2 shows the results of color measurements for Comparative Example 3 (in L*a*b*). W represents white, K represents black, R represents red, Y represents yellow, B represents blue, and G represents green.

[0116] Table 1: Color measurement of various color states of the electro-optical device in Example 2. W K R Y B G L* 66.8 13.9 26.5 63.9 33.9 48.7 a* -3.0 11.2 37.6 -12.7 4.2 -21.6 b* 1.2 -8.3 24.0 64.5 -38.8 36.4

[0117] Table 2: Color measurement of various color states of the electro-optical device in Comparative Example 3. W K R Y B G L* 66.6 12.8 27.4 65.4 42.5 53.9 a* -1.0 10.0 33.7 -12.4 -6.4 -12.3 b* 0.6 -3.6 23.3 37.8 -19.3 9.1

[0118] Comparing the data in Tables 1 and 2, it is shown that the creative apparatus exhibits a significantly improved yellow state (64.5 vs. 37.8 b*). Furthermore, the creative apparatus also shows improved red state (37.6 vs. 33.7 a*), blue state (-38.8 vs. -9.3 b*), and green state (-38.8 vs. -12.3 a*).

[0119] Examples 4A, 4B, and 4C: Preparation of a series of yellow electrophoretic particle dispersions

[0120] A series of yellow electrophoretic particle dispersions (4A, 4B, 4C) were prepared using variations of the general synthesis method described in Example 1. For each dispersion, the weight-average molecular weight of the copolymer present on the surface of the yellow pigment particles was adjusted using standard methods. This polymer was formed by the polymerization of 2-vinylnaphthalene, monomethacryloxypropyl-terminated polydimethylsiloxane, and 2,2,2-trifluoroethyl methacrylate. The particles of each dispersion were separated from the medium and dried. The polymer content of the yellow electrophoretic particles in each dispersion was measured by pyrolysis gravimetric analysis. Furthermore, the weight-average molecular weight was measured by extracting the polymer from the dried particles using THF and analyzing the extract by gel permeation chromatography. Table 3 summarizes the polymer content (weight of polymer, based on the weight of the electrophoretic particle) and weight-average molecular weight of each yellow electrophoretic particle from this series.

[0121] Examples 5A, 5B, and 5C: Fabrication of electro-optical devices and evaluation of image persistence.

[0122] The process of Example 2 was repeated to prepare a series of electrophoretic media and corresponding electro-optic devices (5A, 5B, and 5C). The electrophoretic media for each electro-optic device 5A, 5B, and 5C respectively contained yellow dispersions 4A, 4B, and 4C. Image retention for each electro-optic device was measured as follows: the device was switched to six color patches (white, black, red, yellow, blue, and green); the device was inserted into and maintained in the chamber of a Q-Sun Xenon Arc testing machine (supplied by Q-lab) at 50 °C and 35% relative humidity; the device was removed from the Q-Sun chamber and cooled to room temperature; the electro-optic device was switched to its white state; and the white color (CIELAB) of each patch was measured using a spectrophotometer. Image retention was measured as the difference between the maximum and minimum b*. This is represented by Δb* in CIELAB. Devices with a smaller Δb* (in CIELAB) have less image retention than devices with a larger Δb*. Image retention can also be assessed by visually inspecting the display. Compared with its reference, the device displaying a stronger yellow hue has more image retention than the device displaying a weaker yellow hue compared with its reference. The image retention assessment results of the electro-optical devices 5A, 5B and 5C are provided in Table 4.

[0123] Table 3: Polymer properties of polymers on the surface of yellow particles Polymer content (wt%, based on particle weight) Weight-average molecular weight (Da) Example 4A 5.1 47,000 Example 4B 3.0 55,500 Example 4C 4.2 83,900

[0124] Table 4: Image Residual Assessment Δb* of exposed surface relative to unexposed surface Visual inspection of exposed but unexposed surfaces Example 5A 10.8 yellow hue Example 5B 3.6 Noticeably less yellow hue Example 5C Noticeably less yellow hue

[0125] The evaluation results in Table 4 illustrate that electro-optic devices containing electrophoretic media with yellow electrophoretic particles exhibit significantly less image retention, wherein the surface of the particles comprises polymers with a weight average molecular weight greater than 55,000 Da.

[0126] Example 6. Preparation of creative magenta particles.

[0127] The preparation of Example 1 was repeated, but Pigment Red 122 was used as the organic pigment core, wherein the polymer of the shell was formed from 2-vinylnaphthalene monomer. Three different experiments, 6A, 6B, and 6C, were performed, varying the polymer content of the magenta particles. The particles from Example 6A contained 19% by weight of polymer, based on the weight of the particles (2.5 mmol of monomer per gram of pigment). The particles from Example 6B contained 48% by weight of polymer, based on the weight of the particles (5.0 mmol of monomer per gram of pigment). The particles from Example 6C contained 38% by weight of polymer, based on the weight of the particles (4.0 mmol of monomer per gram of pigment). The polymer content, weight-average molecular weight (Mw), particle size, and zeta potential were determined for each example, as shown in Table 5.

[0128] Table 5. Property evaluation of magenta particles Example Monomer / Pigment polymer content Mw Particle size (µm) Zeta potential (mV) Example 6A 2.5mmol / g 19% 79,900 0.30 35 Example 6B 5.0 mmol / g 48% 257,500 0.31 35 Example 6C 4.0 mmol / g 38% 185,804 0.29 31

[0129] Example 7. Fabrication and stability evaluation of an innovative electro-optic device.

[0130] The electrophoretic medium was prepared using the following: a charge control agent, a hydrocarbon solvent, positively charged magenta particles from Example 6A, positively charged cyan particles (as described in Example 7 of U.S. Patent No. 10,509,293), slightly negatively charged yellow particles (pigment yellow 155, the surface of which was treated with a polymer formed by the polymerization of poly(dimethylsiloxane) terminated in methyl methacrylate and monomethacrylate; the polymer content was 25% by weight, based on the weight of the particles), negatively charged white particles (as described in Example 1 of U.S. Patent No. 8,582,196), and the charge control agent CCA-111 (a cationic charge control agent of CCA111 from Example 1 of patent application US 2020 / 0355978). This electrophoretic medium was used to prepare a microcellular electro-optic device. The electro-optical device was driven to a white state, and the color was measured immediately (t0) and after 24 hours (t24) using a color computer, and reported as ΔE (the color difference from t0 to t24, measured in CIELAB).

[0131] Comparative Example 8. Fabrication and stability evaluation of a comparative electro-optic device.

[0132] The procedure of Example 7 was repeated, but for the comparative electrophoresis medium, control magenta particles were used instead of the magenta particles from Example 6A. The control magenta object comprised a core and a shell, the core containing the same pigment red 122 used in Example 6A, and the shell being formed by treating the magenta pigment with vinyl benzyl chloride followed by methyl methacrylate graft polymerization (as described in Example 1 of U.S. Patent No. 9,697,778). A microcellular electro-optic device was prepared using this electrophoresis medium. The electro-optic device was driven to a white state, and the color was measured immediately (t0) and after 24 hours (t24) using a color computer, and reported in DE (color difference from t0 to t24, measured in CIELAB).

[0133] Stability evaluation of the white state of Examples 7 and 8. It was found that the white state of the inventive device of Example 7 was more stable after 24 hours than that of the device of Example 8, as shown in Table 6. In particular, the color change from t0 to t24, as indicated by DE, showed that the white state of the device of Comparative Example 8 was significantly greater than that of the device of Inventive Example 6. The white state of the device of Comparative Example 8 shifted to a reddish hue within 24 hours.

[0134] Table 6: Color changes of the white state over time. Electro-optical devices Magenta of the electrophoretic medium ΔE Example 7 Example 6A 3.1 Comparative Example 8 Comparison 10.8

[0135] The evaluation results of the above-described inventive and comparative embodiments demonstrate that, in terms of image quality and stability, the electro-optic device containing the inventive electrophoretic medium has significantly improved electro-optic performance compared to the control electrophoretic medium.

[0136] 100: Electro-optical device / equipment 101: First electrode layer 102: Electro-optic material layer 103: Second electrode layer 104: First adhesive layer 105: Second adhesive layer 112: Microcapsules 122: Electrophoretic medium 132: Polymer adhesives 150: Viewing side 200: Electro-optical device 202: Electro-optic material layer 204: Adhesive layer 212: microcell 232: Sealing layer 242: Bottom 250: Viewing side 252: Partition wall 262: Second Type Particle 272: Type I Particles 300: Electro-optical device / equipment 400: Compositions comprising thermoplastics, thermosettings, or precursors thereof. 401: Conductive film 402:Male model 403: Microcell 404: website 500: Microcell Array 501a: Radiation-curable materials 501b: Partition / Exposed Area 502: Conductor film / substrate conductor film / conductor / substrate conductor 503: Supported substrate mesh / substrate 504: Dark square / opaque area 505: Transparent Area 506: Mask / Light Mask 507: Microcell 510: Microcell Array 511a: Radiation-curable materials 511b: Partition wall material 512: Substrate conductor film / substrate conductor / conductor line pattern / conductor line 513: Substrate 514: Line 515: Space 516: Second Light Mask 517: Microcell 640: Microcell Array 660: Microcell 661: Microcellular septum 662: Primer Coating 663: Substrate 664: Electrophoretic medium 665: Particles 666: Polymer 668: Repair Layer

Claims

1. An electrophoretic medium comprising a nonpolar liquid, a plurality of first-type particles and a plurality of second-type particles, each of the plurality of first-type particles comprising a core and a shell; the core comprising a pigment having a surface, the pigment being an organic or inorganic pigment; the shell comprising a polymer, the polymer being a homopolymer or copolymer, the homopolymer being formed by polymerization of vinylnaphthalene, the copolymer being formed by polymerization of vinylnaphthalene and a first monomer, the homopolymer or copolymer being in contact with the surface of the pigment, wherein the shell bodies of the plurality of first-type particles and the plurality of second-type particles are in contact with the nonpolar liquid, and wherein the plurality of first-type particles have a charge polarity opposite to that of the plurality of second-type particles.

2. The electrophoretic medium of claim 1, wherein the polymer of the shell has a weight average molecular weight of 55,000 to 400,000 Da.

3. The electrophoretic medium of claim 1, wherein the vinylnaphthalene is selected from the group consisting of 1-vinylnaphthalene, 2-vinylnaphthalene, substituted 1-vinylnaphthalene and substituted 2-vinylnaphthalene, wherein the substituted 1-vinylnaphthalene and the substituted 2-vinylnaphthalene have one or more substituents in addition to the vinyl substituent on the aromatic carbon of the naphthalene ring.

4. The electrophoretic medium of claim 3, wherein the one or more substituents are selected from the group consisting of: halogen, alkoxy, alkyl, nitro, carboxyl, hydroxy, sulfonic acid, sulfonate / salt and amino.

5. The electrophoretic medium of claim 1, wherein the first monomer has a molecular structure comprising functional groups selected from the group consisting of vinyl groups, acrylate groups, and methacrylate groups.

6. The electrophoretic medium of claim 1, wherein the first monomolecular macromonomer has a molecular structure including a first functional group and a second functional group, the first functional group being polydimethylsiloxane, and the second functional group being vinyl, methacrylate / base, or acrylate / base.

7. The electrophoretic medium of claim 1, wherein the first single system is selected from the group consisting of: methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, ethylhexyl methacrylate, ethylhexyl acrylate, lauryl methacrylate, lauryl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,2-trifluoroethyl acrylate, styrene, and α-methylstyrene.

8. The electrophoretic medium of claim 1, wherein the copolymer is formed from the vinyl naphthalene, the first monomer and the second monomer, wherein the first monomer is 2,2,2-trifluoroethyl methacrylate and the second monomer has a molecular structure including (i) polydimethylsiloxane and (ii) vinyl functional groups, acrylate / salt functional groups or methacrylate / salt functional groups.

9. The electrophoretic medium of claim 8, wherein the weight-average molecular weight of the copolymer is 55,000 to 250,000 Da.

10. The electrophoretic medium of claim 8, wherein the second single system is a polydimethylsiloxane with monomethacrylic oxypropyl terminals.

11. The electrophoretic medium of claim 1 further comprises a plurality of third-type particles and a plurality of fourth-type particles.

12. The electrophoretic medium of claim 11, wherein each of the plurality of first type particles contains an organic pigment, each of the second and third type particles contains an organic pigment, and each of the plurality of fourth type particles contains an inorganic pigment.

13. The electrophoretic medium of claim 11, wherein the first, second and third type particles have a first charge polarity, the fourth type particles have a second charge polarity, and the first charge polarity is opposite to the second charge polarity.

14. The electrophoretic medium of claim 11, wherein the first and third type particles have a first charge polarity, wherein the second and fourth type particles have a second charge polarity, and wherein the first charge polarity is opposite to the second charge polarity.

15. The electrophoretic medium of claim 11, wherein the colors of the first, second and third type particles are independently selected from the group consisting of cyan, magenta, yellow, blue, green and red, and wherein the color of the fourth type particles is white.

16. The electrophoretic medium of claim 11, wherein the first, second and third type particles are independently selected from the group consisting of: azo pigments, phthalocyanine pigments, quinacrine pigments, perylene pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, isoindoline pigments, anthrone pigments, indanthrone pigments, rhodamine pigments, benzinamine pigments, carbon black pigments, and mixtures thereof.

17. An electro-optic device comprising a first light-transmitting electrode layer, an electro-optic material layer comprising an electrophoretic medium as claimed in any one of claims 1 to 16, and a second electrode layer, wherein the electro-optic material layer comprises a plurality of microcapsules or a plurality of microcells, each microcapsule of the plurality of microcapsules or each microcell of the plurality of microcells comprising the electrophoretic medium.

18. A method for manufacturing an electrophoretic medium, the electrophoretic medium comprising a nonpolar liquid and a plurality of first-type particles, the first-type particles having a core and a shell, the shells of the plurality of first-type particles being in contact with the nonpolar liquid, the plurality of first-type particles being charged particles, the manufacturing method comprising the following steps: providing a first dispersion containing an organic pigment in a first organic solvent; adding vinylnaphthalene, a first monomer and a free radical initiator to the first dispersion to form the first-type particles; washing the first-type particles with a second organic solvent; and dispersing the washed particles in the nonpolar liquid.

19. A method for manufacturing an electrophoretic medium as claimed in claim 18, wherein the first dispersion further comprises a charge control agent.

20. The method for manufacturing the electrophoretic medium of claim 18 further comprises the following step: adding a charge control agent to the cleaned particles in a dispersion in the nonpolar liquid.

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