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

Abstract

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

Description

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 617,957, filed January 5, 2024, which is incorporated in its entirety by reference, along with all other patents and patent applications disclosed herein. Invention Field

[0003] 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. The particles can be used as electrophoretic media in electro-optic devices. Background of the Invention

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

[0006] Some electro-optic materials are solid in the sense that they have a solid outer surface, although such materials may and often do have liquid- or gas-filled internal spaces. For convenience, such displays using solid electro-optic materials will be referred to below as "solid-state electro-optic displays." Therefore, the term "solid-state electro-optic display" includes rotating dual-color element displays, encapsulated electrophoretic displays, microcell electrophoretic displays, and encapsulated liquid crystal displays.

[0007] The terms “bistable” and “bistable” are used herein in their conventional sense in the art to refer to a display comprising display elements having a first display state and a second display state that are different in at least one optical property, and such that after any given element has been driven to present its first or second display state by an addressing pulse of finite duration, the state will persist for at least several times, for example, at least four times, the minimum duration of the addressing pulse required to change the state of the display element after the addressing pulse has terminated. U.S. Patent No. 7,170,670 shows that some particle-based electrophoretic displays capable of displaying grayscale are stable not only in their extreme black and white states but also in their intermediate gray states, and this is also true for some other types of electro-optical displays. This type of display is properly referred to as “multistable” rather than bistable, but for convenience, the term “bistable” as used herein can be used to encompass both bistable and multistable displays.

[0008] Electro-optic displays, a type of display that has been the subject of in-depth research and development for many years, are particle-based electrophoretic displays, in which multiple charged particles move through a fluid under the influence of an electric field. Compared to 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 application. For example, the particles constituting an electrophoretic display tend to settle, leading to a short lifespan for these displays.

[0009] As mentioned above, electrophoretic media require the presence of a fluid. In most prior art electrophoretic media, this fluid is a liquid, but gaseous fluids can also be used to produce electrophoretic media; 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. Patents 7,321,459 and 7,236,291. When such gas-based electrophoretic media are used in orientations that allow particle sedimentation, for example, in markings where the media is positioned in a vertical plane, the media appears to be prone to the same type of problems as liquid-based electrophoretic media due to such sedimentation. In fact, particle sedimentation appears to be a more serious problem in gas-based electrophoresis media than in liquid-based electrophoresis media because the lower viscosity of gaseous suspensions compared to liquid suspensions causes electrophoretic particles to settle more quickly.

[0010] Numerous patents and applications assigned to or attributed to MIT, E Ink Corporation, E Ink California, LLC., and related companies describe various techniques used in encapsulated electrophoretic media and microcell electrophoretic media, as well as other electro-optic media. Encapsulated electrophoretic media comprise numerous vesicles, each vesicle itself comprising an inner phase and a vesicle wall surrounding the inner phase, the inner phase containing particles that electrophoretically move in a fluid medium. Typically, the vesicles themselves are held within a polymer binder to form a coherent layer between two electrodes. In microcell electrophoretic displays, charged particles and fluid are not encapsulated within microcapsules but are retained within a carrier medium, typically multiple cavities formed within a polymer film. The techniques described in these patents and applications include:

[0011] (a) Electrophoretic particles, fluids, and fluid additives; see, for example, 5,961,804; 6,017,584; 6,120,588; 6,120,839; 6,262,706; 6,262,833; 6,300,932; 6,323,989; 6,377,387; 6,515,649; 6,538,801; 6,580,545; 6,652,075; 6,693,620; 6,721,083; 6,727,881; 6,822,782; 6,831,771; 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;7,277,21 8; 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 U.S. Patents 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; 10,147,366; and 10,514,583; and U.S. Patents 2003 / 0048522; 2003 / 0151029; 2003 / 0164480; 2004 / 0030125; 2004 / 0105036; 2005 / 0012980; 2009 / 0009852;U.S. Patent Application Publications Nos. 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.

[0012] (b) Encapsulation, adhesives and encapsulation methods; see, for example, 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; 7,148,128; U.S. Patent Nos. 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 Publications Nos. 2005 / 0156340; 2007 / 0091417; and 2009 / 0122389.

[0013] (c) Micro-unit structures, wall materials, and methods of forming micro-units; see, for example, 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; 6,870,662; 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 U.S. Patent Nos. 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 Publications Nos. 2003 / 0203101; 2014 / 0050814; and 2016 / 0059442.

[0014] (d) Methods for filling and sealing microcells; see, for example, 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 U.S. Patent Nos. 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 Publications Nos. 2002 / 0188053; 2004 / 0120024; 2004 / 0219306; and 2015 / 0098124.

[0015] (e) Films and sub-assemblies containing electro-optic materials; see, for example, pp. 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; 7,843,621; 7,84 U.S. Patent Nos. 3,624; 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 Publications Nos. 2005 / 0122563; 2007 / 0237962; and 2011 / 0164301.

[0016] (f) Backplanes, adhesive layers and other auxiliary layers and methods used in displays; see, for example, 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; 7,012,600; 7,01 2,735; 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; 7,492,497; 7,53 5,624; 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; 8,362,488; 8,39 5,836; 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; 8,754,859; 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 U.S. Patents Nos. 041, 10,509,294, and 10,613,407; and Nos. 2002 / 0060321, 2004 / 0085619, 2004 / 0105036, 2005 / 0122306, 2005 / 0122563, 2006 / 0255322, 2009 / 0122389, 2010 / 0177396, and 2011 U.S. Patent Application Publications Nos. 0164301; 2011 / 0292319; 2014 / 0192000; 2014 / 0210701; 2014 / 0368753; and 2016 / 0077375; and International Patent Application Publications Nos. WO2000 / 038000; WO2000 / 005704; and WO1999 / 067678.

[0017] (g) Color formation and color adjustment; see, for example, 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;8,503,0 63; 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; 8,830,559; 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;9,195,1 U.S. Patents Nos. 11; 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. Patents Nos. 2008 / 0043318; 2008 / 00489 70; 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;U.S. Patent Application Publications Nos. 2016 / 0026062, 2016 / 0048054, 2016 / 0116816, 2016 / 0116818, and 2016 / 0140909.

[0018] (h) Methods for driving a display; see, for example, sections 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; 7,312,7 94; 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; 7,683,606; 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;8,125,501;8,1 39,050; 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; 8,643,595; 8,665,206; 8,681,191 U.S. Patents Nos. 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, 9,218,773, 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, and 9,412,314;and 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; 2009 / 0322 721; 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; 2013 / 00633 33; 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; 2014 / 034073 4; U.S. Patent Application Publications Nos. 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.

[0019] (i) Applications of displays; see, for example, pp. 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; 9,188,829; and 9,197, U.S. Patent No. 704; and U.S. Patent Application Publications 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 Patent Application Publication No. WO00 / 36560.

[0020] (j) Non-electrophoretic displays, such as those specified in 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 8,994,705. See, for example, U.S. Patent Nos. 2005 / 0099575; 2006 / 0262249; 2007 / 0042135; 2007 / 0153360; 2008 / 0020007; 2012 / 0293858; and 2015 / 0277160; as well as applications of packaging and microcell technologies other than displays; see, for example, U.S. Patent No. 7,615,325; and U.S. Patent Application Publications Nos. 2015 / 0005720 and 2016 / 0012710.

[0021] Many of the aforementioned patents and applications recognize that the walls surrounding discrete microcapsules in an encapsulated electrophoretic medium can be replaced by a continuous phase, thereby producing so-called polymer-dispersed electrophoretic displays, wherein the electrophoretic medium comprises discrete droplets of multiple electrophoretic fluids and a continuous phase of polymeric material, and recognize that although the discrete capsule membrane is not associated with each individual droplet, the discrete droplets of electrophoretic fluids within such a polymer-dispersed electrophoretic display can also be considered as capsules or microcapsules; see, for example, U.S. Patent No. 6,866,760 mentioned above. Therefore, for the purposes of this application, such polymer-dispersed electrophoretic media are considered a subtype of encapsulated electrophoretic media.

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

[0023] Encapsulated electrophoretic displays typically do not suffer from the aggregation and sedimentation failure modes of conventional electrophoretic apparatus 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 used to include all forms of printing and coating, including but not limited to: volumetric coating, such as patch die coating, slot or extrusion coating, cascade coating, curtain coating; roll coating, such as roller-blade 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 can be flexible. Furthermore, because the display medium can be printed (using various methods), the display itself can be manufactured at low cost.

[0024] Electrophoretic media contain charged pigment particles in a nonpolar liquid, and the image quality of an electrophoresis apparatus containing such a medium may be degraded due to the aggregation of charged particles, especially 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, an electrophoretic medium may contain charged particles of four different colors, such as blue, red, yellow, and white. In such a medium, aggregation between blue-red and blue-yellow particles prevents complete separation of the electrophoretic particles during apparatus operation, resulting in a lower chromatic color state. Similarly, an electrophoretic medium may contain charged particles containing cyan, magenta, yellow, and white pigments, and aggregation between cyan-magenta, cyan-yellow, and magenta-yellow pigments can adversely affect the electro-optical performance of the apparatus. Aggregation between organic pigment particles can be mitigated to some extent if one or more organic pigments, such as cyan or blue pigments, are replaced with inorganic pigments with similar color properties. However, inorganic pigments generally do not provide colors with high chromaticity compared to organic pigments. Therefore, there is a need to improve the particles used in the electrophoretic medium. Furthermore, the image initially formed by the electro-optic device may change over time. For example, the white state of the device may transform into a slightly tinted white state, thereby reducing the overall image quality. Therefore, there is a need to design electrophoretic particles in the electrophoretic medium that contribute to a more stable optical state. The inventors of this invention unexpectedly discovered that using particles comprising (1) a core containing pigment particles and (2) a shell containing a polymer formed from a monomer, wherein the monomer is vinylnaphthalene, significantly improves the electro-optic performance of the corresponding device by providing greater color saturation and a more stable optical state over time.

[0025] One of the problems occasionally observed in electrophoretic displays under certain conditions is "image retention." Image retention occurs when a type of electrophoretic particle is strongly adsorbed onto the surface of microcells in an electro-optic material layer, and these particles are not completely removed when an electric field is applied, thus preventing the microcells from effectively switching from a first color state to a second color state. In such cases, the second color state is contaminated by the first color state, degrading the image quality of the electro-optic display. In the past, this problem was mitigated by using electrophoretic media that included filler particles in addition to the electrophoretic charged particles (see U.S. Patent 8,115,729B2). However, the addition of filler particles also increases the viscosity of the electrophoretic media, thereby increasing the transition speed between color states and also increasing the voltage required for switching between optical states. The inventors of this invention unexpectedly discovered that by surface-treating the corresponding electrophoretic particles with a polymer formed from vinylnaphthalene monomers and polydimethylsiloxane macromonomers, image retention can be mitigated without affecting the viscosity of the electrophoretic media, the polymer having a weight-average molecular weight greater than 55,000 Daltons. Invention Overview

[0027] According to one aspect 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 pigment or an inorganic pigment. The shell comprises a polymer, which is a homopolymer or a 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 Da, 55,000 to 250,000 Da, or 55,000 to 200,000 Da. The polymer of the shell may have a weight-average molecular weight greater than 55,000.

[0028] Vinylnaphthalene can be 1-vinylnaphthalene, 2-vinylnaphthalene, substituted 1-vinylnaphthalene, and substituted 2-vinylnaphthalene, wherein the substituted 1-vinylnaphthalene and 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 halogens, alkoxy groups, alkyl groups, nitro groups, carboxyl groups, hydroxyl groups, sulfonic acid groups, sulfonate groups, and amino groups.

[0029] The first monomer can be a macromonomer. The macromonomer can have a molecular structure including a first functional group and a second functional group. The first functional group can be polydimethylsiloxane, and the second functional group can be a vinyl group, a methacrylate group, or an acrylate group.

[0030] The first monomer may have a molecular structure, which includes functional groups selected from vinyl, acrylate, and methacrylate groups. The first monomer may be selected from 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.

[0031] The copolymer can be formed from vinylnaphthalene, a first monomer, and a second monomer, wherein the first monomer is 2,2,2-trifluoroethyl methacrylate and the second monomer has a molecular structure comprising (i) a polydimethylsiloxane and (ii) a vinyl functional group, an acrylate functional group, or a methacrylate functional group, 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, a first monomer, and a second monomer, wherein the first monomer is 2,2,2-trifluoroethyl methacrylate and the second monomer is a monomethacryloyloxypropyl-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, a first monomer, a second monomer, and a third monomer.

[0032] The electrophoretic medium may also include multiple third-type particles and multiple fourth-type particles. First and second-type particles may contain organic pigments, third-type particles may contain organic pigments, and fourth-type particles may contain inorganic pigments. First, second, and third-type particles may have a first charge polarity, and fourth-type particles may have a second charge polarity; the first charge polarity may be opposite to the second charge polarity.

[0033] The first, second, and third types of particles can be independently selected from cyan, magenta, yellow, blue, green, and red, and the fourth type of particle is white.

[0034] The first, second, and third types of particles can be independently selected from azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, isoindoline pigments, anthrone pigments, indanone pigments, rhodamine pigments, aniline pigments, carbon black pigments, and mixtures thereof.

[0035] The first, second, and third types of particles can be independently selected from 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 Pigment 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, 41; Pigment Orange 5, 13, 34, 36, 38, 43, 61, 62, 64, 68, 67, 72, 73 and 74 and mixtures thereof.

[0036] The electrophoretic medium may include particles of types 1, 2, 3, 4, and 5. Type 5 particles may contain inorganic or organic pigments. Types 1 and 4 particles may have a charge polarity opposite to that of types 2, 3, and 5 particles. Types 1 and 4 particles may be negatively charged, while types 2, 3, and 4 particles may be positively charged. If types 1 and 4 particles are negatively charged, then type 1 particles may have a more negative zeta potential than type 4 particles. If types 2, 3, and 5 particles are positively charged, then type 5 particles may have a greater zeta potential than types 2 and 3 particles. The color of types 4 and 5 particles may be selected from white and black.

[0037] According to another aspect of the invention, the electro-optic device includes a first transparent electrode layer, an electro-optic material layer comprising an 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 includes 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 of vinylnaphthalene. The copolymer is formed of vinylnaphthalene and a first monomer. The homopolymer or copolymer is in contact with the surface of the pigment. The vinylnaphthalene can be 1-vinylnaphthalene, 2-vinylnaphthalene, substituted 1-vinylnaphthalene, and substituted 2-vinylnaphthalene, wherein the substituted 1-vinylnaphthalene and substituted 2-vinylnaphthalene have one or more substituents in addition to vinyl substituents on the aromatic carbon of the naphthalene ring. The one or more substituents can be selected from halogens, alkoxy groups, alkyl groups, nitro groups, carboxyl groups, hydroxyl groups, sulfonic acid groups, sulfonate groups, and amino groups.

[0038] 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 steps of: (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 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 washed particle dispersion in the nonpolar liquid. The method may further comprise the step of adding a second dispersion comprising an organic or inorganic pigment in the nonpolar liquid to the washed particle dispersion in the nonpolar liquid. Brief description of the attached diagram

[0040] Various aspects and embodiments of this application will be described with reference to the following accompanying drawings. It should be understood that the drawings are not necessarily drawn to scale.

[0041] Figure 1 This is a side view of a portion of an electro-optic device comprising an electrophoretic medium encapsulated in multiple microcapsules. The device includes a first transparent electrode layer, an electrophoretic material layer, a first adhesive layer, and a second electrode layer.

[0042] Figure 2 This is a side view of a portion of an electro-optic device comprising an electrophoretic medium encapsulated in multiple microcapsules. The device includes a first transparent electrode layer, a second adhesive layer, an electrophoretic material layer, and a second electrode layer.

[0043] Figure 3 This is a side view of a portion of an electro-optic device, which includes an electrophoretic medium encapsulated within multiple microcells. The device includes a first transparent electrode layer, a microcell layer, an adhesive layer, and a second electrode layer.

[0044] Figure 4 A method for fabricating microcells for use in this invention using a roll-to-roll process is shown.

[0045] Figures 5A and 5B detail the production of microcells for electro-optic devices using photolithography through a photomask coated with a conductive film of a thermosetting precursor.

[0046] Figures 5C and 5D detail alternative embodiments in which microcells for electro-optic devices are fabricated using photolithography. In Figures 5C and 5D, a combination of top and bottom exposures is used, whereby the separator is cured in one lateral direction by exposure through a top photomask and in another lateral direction by bottom exposure through an opaque substrate conductor film.

[0047] Figures 6A-6D This describes the steps for filling and sealing microcell arrays used in electro-optic devices. Invention Details

[0049] "Dispersion polymerization" is a polymerization process involving soluble starting materials (including monomers, initiators, etc.), in which the polymer product precipitates out during the polymerization process. In the manufacture of electrophoretic core-shell particles, the polymerization reaction takes place in a pigment dispersion, allowing the polymer formed by dispersion polymerization to precipitate on the surface of the pigment particles.

[0050] 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.

[0051] The term "vinylnaphthalene" refers to a molecule having a vinyl group bonded to an aromatic carbon atom in the naphthalene aromatic system. The naphthalene aromatic system is represented by Formula 1. The naphthalene aromatic system (Formula 1) comprises a fused aromatic ring system with 10 aromatic carbon atoms. The conventional numbering of the carbon atoms in naphthalene is provided in Formula 1. The vinyl group is represented by the molecular structure of Formula 2. A simpler equivalent representation of the vinyl group is: -CH=CH2.

[0052] The term "substituted 1-vinylnaphthalene" refers to a molecule containing a naphthalene aromatic system, a vinyl group bonded to an aromatic carbon atom of the naphthalene aromatic system, and one or more substituents bonded to the aromatic carbon atom of the naphthalene aromatic system. That is, the molecular structure of substituted 1-vinylnaphthalene comprises at least two substituents bonded to an aromatic carbon atom of the naphthalene aromatic system, one of which is a vinyl group bonded to a carbon atom at position 1 of the naphthalene aromatic system (refer to Formula 1). In other words, in addition to the vinyl substituent, "substituted 1-vinylnaphthalene" has one or more substituents on the aromatic carbon atom of the naphthalene aromatic system. The one or more substituents cannot be hydrogen.

[0053] The term "substituted 2-vinylnaphthalene" refers to a molecule containing a naphthalene aromatic system, a vinyl group bonded to an aromatic carbon atom of the naphthalene aromatic system, and one or more substituents bonded to the aromatic carbon atom of the naphthalene aromatic system. That is, the molecular structure of substituted 2-vinylnaphthalene comprises at least two substituents bonded to an 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 (refer to Formula 1). In other words, in addition to the vinyl substituent, "substituted 2-vinylnaphthalene" has one or more substituents on the aromatic carbon atom of the naphthalene aromatic system. The one or more substituents cannot be hydrogen.

[0054]

[0055]

[0056] For the purposes of this invention, the numbering of substituents in vinylnaphthalene may not strictly follow the IUPAC rules. For the purposes of this invention, 1-vinylnaphthalene 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-vinylnaphthalene is any naphthalene having a vinyl group covalently bonded to an aromatic carbon of the naphthalene aromatic system, wherein the aromatic carbon is not adjacent to carbon 4a or carbon 8a of the naphthalene aromatic system. This means that, for the purposes of this invention, the numbering of vinyl groups takes precedence over any other groups covalently bonded to the aromatic carbon of the naphthalene aromatic system. That is, 2-chloro-6-naphthalene (as shown in Formula 3) is still considered 2-vinylnaphthalene because the vinyl group in this compound is covalently bonded to an aromatic carbon of the naphthalene aromatic system, wherein the aromatic carbon is not adjacent to carbon 4a or 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 to be 2-vinylnaphthalene because it is equivalent to the less “officially recognized” name “2-vinyl-6-chloronaphthalene”.

[0057]

[0058] The term "macromere" (or "macromonomer") is used to refer to a relatively high molecular weight substance (above 500 g / mol) with a single functional group that can participate in polymerization. In other words, a macromonomer can act as a monomer, even though it has a high molecular weight or internal monomer unit in its molecular structure. Therefore, a macromonomer can be considered a polymer. Typically, a macromonomer contributes a single monomer unit to the resulting polymer.

[0059] For the purposes of this application, the term "copolymer" is a polymer comprising two or more distinct repeating units. A macromonomer is considered to contain repeating units. Copolymers can be formed from two or more different types of monomers. For example, a ternary copolymer is considered a copolymer for the purposes of this invention. That is, copolymers can be formed from two, three, four, or other different types of monomers.

[0060] An example of an electro-optic device includes an electro-optic material layer containing an electrophoretic medium encapsulated in a microcapsule or microcell, as described in U.S. Patent No. 6,982,178. Figure 1 A side view showing an example of the structure of a portion of an electro-optic device comprising microcapsules is provided. 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 including a plurality of pixel electrodes. The first adhesive layer 104 connects the electro-optic material layer 102 to the second electrode layer 103. The electro-optic material layer 102 includes a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and includes an electrophoretic medium 122 having particles in a nonpolar liquid. Typically, the multiple microcapsules are retained within a polymer 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-panel laminate, as described in the background of the invention.

[0061] Figure 2 Another example of an electro-optical device is shown in the figure. Figure 2A side view illustrating 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 including light-transmitting electrodes, a second adhesive layer 105, an electro-optic material layer 102, a first adhesive layer 104, and a second electrode layer 103 including a plurality of pixel electrodes. The second adhesive layer 105 connects the first electrode layer 101 to the electro-optic material layer 102. The first adhesive layer 104 connects the electro-optic material layer 102 to the second electrode layer. The electro-optic material layer 102 includes a plurality of microcapsules 112. Each microcapsule has a microcapsule wall and includes an electrophoretic medium 122 having particles in a nonpolar liquid. Typically, the plurality of microcapsules are retained within a polymer adhesive 132. The electro-optic device 200 may be constructed from a dual release sheet as described above.

[0062] Figure 1 and Figure 2 The microencapsulated electro-optic device may also include a light-transmitting front substrate ( Figure 1 and Figure 2 (not shown in the image), which is adjacent to the first electrode layer 101, wherein the electrode layer is disposed between the front substrate and the electro-optic material layer (for Figure 1 (the device) or between the front substrate and the second adhesive layer (for 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 also include one or more additional layers, such as a protective layer that absorbs ultraviolet radiation, a barrier layer that prevents oxygen or moisture from entering the device, and an anti-reflective coating that improves the optical properties of the device.

[0063] Figure 3 An example of an electro-optic device including micro-units is illustrated. Figure 3 The electro-optic device 300 sequentially includes a first electrode layer 101, an electro-optic material layer 202, an adhesive layer 204, and a second electrode layer 103 including multiple pixel electrodes. The adhesive layer 204 connects the sealing layer 232 of the electro-optic material layer 202 to the second electrode layer 103. The electro-optic material layer 202 of the electro-optic device 300 includes multiple micro-units 212 and a sealing layer 232. Each micro-unit 212 has a bottom 242, a partition wall 252, and an opening, and the sealing layer 232 spans the opening of each micro-unit. Each micro-unit 212 contains an electrophoretic medium 122. The electrophoretic medium 122 contains multiple first-type particles 272 and multiple second-type particles 262 in a non-polar liquid. A viewer can view an image of the device 300 from a viewing side 250.

[0064] Figure 3 The micro-unit electro-optic device may also include a light-transmitting front substrate ( Figure 3(Not shown in the image), it is 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 can be a plastic film, such as a polyethylene terephthalate (PET) sheet having a thickness of 25 to 200 μm. The light-transmitting front substrate may also include one or more additional layers, such as a protective layer for absorbing ultraviolet radiation, a barrier layer for preventing oxygen or moisture from entering the device, and an anti-reflective coating for improving the optical properties of the device.

[0065] exist Figure 1 , 2 In the electro-optic device of 3, the first electrode layer may be a conductive layer having a thin, continuous coating of a conductive material that has minimal inherent absorption of electromagnetic radiation in the visible spectrum range. The conductive material may be, for example, indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene)poly(styrene sulfonate) (PEDOT:PSS), graphene, etc.

[0066] Figure 1 , 2 The electrophoretic medium 122 of the electro-optic device shown in Figure 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 includes 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 also comprise a plurality of third-type particles and a plurality of fourth-type particles. The electrophoretic medium 122 may also 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 comprise 0.1% to 50% of the volume of the nonpolar liquid, preferably 0.5% to 15%.

[0067] The electrophoretic medium of this invention may contain a charge control agent (CCA). CCA controls the charge on the electrophoretic particles. 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). CCA can complex with or adsorb onto charged particles. It is believed that CCA forms reverse micelles in the electrophoretic medium. It is the small amount of charged reverse micelles that causes the conductivity in the medium. Reverse micelles contain a polar core, the size of which can vary from 1 nm to tens of nanometers, and can have spherical, cylindrical, or other geometries, surrounded by the nonpolar tail groups of the CCA molecule. In the electrophoretic medium, three phases can generally be distinguished: solid particles with surfaces, a highly polar phase distributed in the form of extremely small droplets (reverse micelles), and a continuous phase containing a nonpolar fluid. After an electric field is applied, both the electrophoretic particles and the charged reverse micelles can move through the fluid. Therefore, there are two parallel paths for conducting electricity through the fluid (which itself typically has extremely low conductivity). The charge control agent content in the electrophoresis medium can be 0.1% to 8% by weight, 0.3% to 7% by weight, 0.5% to 5% by weight, 0.6% to 4% by weight, 0.7% to 3% by weight, or 0.8% to 2% by weight of the electrophoresis medium.

[0068] The electrophoretic medium of the present invention comprises particles suspended in a nonpolar liquid. The nonpolar liquid may be transparent and colorless. For high particle mobility, its dielectric constant is preferably from about 2 to about 30, more preferably from about 2 to about 15. Examples of suitable dielectric solvents include hydrocarbons such as isoparaffin, decalin, 5-ethylidene-2-norbornene, fatty oils, paraffin oils, silicone fluids, aromatics (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 Company in St. Paul, Minnesota), low molecular weight halogenated polymers (such as poly(perfluoropropylene oxide) from TCI America in Portland, Oregon), and poly(chlorotrifluoroethylene) (such as Halocarbon from Halocarbon Product Corp. in RiverEdge, New Jersey). Oils), perfluoropolyalkyl ethers (such as KrytoxOils and Greases K-Fluid series from Galden in Ausimont or DuPont in Delaware), and polydimethylsiloxane-based silicone oils (DC-200) from Dow-corning.

[0069] Microcells can be formed using either batch or continuous roll-to-roll processes, as disclosed in U.S. Patent No. 6,933,098. The latter provides a continuous, low-cost, high-throughput manufacturing technique for producing chambers for a variety of applications, including electro-optical devices. Figure 4 As shown, the microcell array suitable for this invention can be manufactured using microimprinting. The male mold 402 can be placed above the web 404, as... Figure 4 As shown, it may be placed below web 404 (not shown); however, other arrangements are also possible. See U.S. Patent No. 7,715,088, the entire contents of which are incorporated herein by reference. The conductive substrate may be constructed by forming a conductive film 401 (first electrode) on a polymer substrate, which serves as a backing for the 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 embossed by a male die in the form of a roller, plate, or strip at a temperature above the glass transition temperature of the thermoplastic or thermosetting precursor layer.

[0070] Thermoplastic or thermosetting precursors used to prepare microunits can be multifunctional acrylates or methacrylates, vinyl ethers, epoxides and their oligomers or polymers, etc. Combinations of multifunctional epoxides and multifunctional acrylates are also very useful for achieving the desired physical and mechanical properties. Crosslinkable oligomers that impart flexibility, such as polyurethane acrylates or polyester acrylates, can be added to improve the flexural strength of the embossed microunits. The composition may contain polymers, oligomers, monomers, and additives, or only oligomers, monomers, and additives. The glass transition temperature (or Tg) of such materials... g The temperature range is typically from about -70°C to about 150°C, preferably from about -20°C to about 50°C. Microembossing processes are typically performed at temperatures above T... g The process is carried out at a specific temperature. A heated male mold or die pressed onto a heated outer shell substrate can be used to control the temperature and pressure of the micro-embossing.

[0071] like Figure 4As shown, demolding is performed during or after the precursor layer curing to expose the microcell array 403. Curing of the precursor layer can be accomplished by cooling, solvent evaporation, radiation crosslinking, heating, or moisture. If curing of the thermosetting precursor is accomplished by UV radiation, UV light can radiate from the bottom or top of the web onto the transparent conductor film. Alternatively, a UV lamp can be placed inside the mold. In this case, the mold must be transparent to allow UV light to radiate onto the thermosetting precursor layer through a pre-patterned male mold. The male mold can be prepared by any suitable method, such as diamond turning or photoresist processing, followed by etching or electroplating. The master template of the male mold can be manufactured by any suitable method, such as electroplating. With the aid of electroplating, a thin layer (typically 3000 Å) of seed metal, such as chrome inconel, is sputtered onto a glass substrate. The mold is then coated with a layer of photoresist and exposed to UV. A mask is placed between the UV and photoresist layers. The exposed areas of the photoresist harden. Unexposed areas are then removed by washing with a suitable solvent. The remaining hardened photoresist is dried and re-sputtered with a thin layer of seed metal. 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 plating. The mold base is typically between about 50 and 400 micrometers. The master template can also be fabricated 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 mold can be fabricated using plastics, ceramics, or metals via photomechanical processing.

[0072] Before applying the UV-curable resin composition, the mold can be treated with a release agent to aid in the demolding process. The UV-curable resin can be degassed before dispensing and may optionally contain a solvent. The solvent, if present, is readily evaporable. The UV-curable resin is dispensed onto the male mold by any suitable method, such as coating, dip coating, casting, etc. The dispenser can be mobile or stationary. A conductor film is applied over the UV-curable resin. If necessary, pressure can be applied to ensure proper bonding between the resin and plastic and to control the thickness of the micro-unit bottom surface. Pressure can be applied using laminating rollers, vacuum molding, pressing devices, or any other similar means. If the male mold is metallic and opaque, the plastic substrate is typically transparent to the photochemical radiation used to cure the resin. Conversely, the male mold can be transparent, and the plastic substrate can be opaque to photochemical radiation. For good transfer of molding features onto the transfer sheet, the conductor film needs to have good adhesion to the UV-curable resin, which should have good release properties to the mold surface.

[0073] Photolithography. Microcells can also be produced using photolithography. Figures 5A and 5B illustrate the photolithography process used to fabricate an array of microcells. As shown in Figures 5A and 5B, the microcell array 500 can be prepared by exposing a radiation-curable material 501a coated on a conductor film 502 using known methods to UV light (or alternatively, other forms of radiation, electron beams, etc.) through a mask 506 to form partition walls 501b corresponding to an image projected through the mask 506. The substrate conductor film 502 is preferably mounted on a supporting substrate web 503, which may comprise a plastic material.

[0074] In the photomask 506 of Figure 5A, dark squares 504 represent opaque areas, and the spaces between the dark squares represent transparent areas 505 of the mask 506. UV radiation passes through the transparent areas 505 onto the radiation-curable material 502a. Exposure is preferably performed directly on the radiation-curable material 502a, i.e., UV radiation does not penetrate the substrate 503 or the substrate conductor 502 (top exposure). Therefore, neither the substrate 503 nor the conductor 502 needs to be transparent to the UV or other radiation wavelengths used.

[0075] 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 using a suitable solvent or developer to form microunits 507. The solvent or developer is selected from those commonly used to dissolve or reduce the viscosity of radiation-curable materials, such as methyl ethyl ketone (MEK), toluene, acetone, isopropanol, etc. The fabrication of the microunits can be similarly achieved by placing a photomask beneath the conductor film / substrate support web, in which case UV light irradiates through the photomask from the bottom, and the substrate needs to be transparent to the radiation.

[0076] Image-based exposure. Figures 5C and 5D illustrate an alternative method for preparing the microcell array of the present invention by image-based exposure. When opaque conductors are used, the conductors can be used as photomasks for bottom-exposure. Durable microcell partitions are formed by additional top-exposure through a second photomask with opaque lines perpendicular to the conductors. Figure 5C illustrates the production of the microcell array 510 of the present invention using the top and bottom exposure principle. The substrate conductor film 512 is opaque and patterned with lines. A radiation-curable material 511a coated on the substrate conductor 512 and the substrate 513 is exposed from the bottom through the conductor pattern 512, which serves as a first photomask. A second exposure is performed from the “top” side through a second photomask 516 with a line pattern perpendicular to the conductors 512. The spaces 515 between the lines 514 are substantially transparent to UV light. In this process, the partition material 511b is cured from bottom to top in a lateral orientation and from top to bottom in a vertical direction, connecting to form an integral microcell 517. As shown in Figure 5D, the unexposed areas are then removed using the solvent or developer described above to expose the micro-unit 517.

[0077] The microunits can be composed of thermoplastic elastomers that are well compatible with the microunits 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 cannot be the same. The numeral n ≥ 1, preferably 1-10. Particularly useful are diblock and triblock copolymers of styrene or oxymethylstyrene, 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, such as the Kraton D and G series (obtained from Kraton Polymer in Houston, Texas), are particularly useful. Crystalline rubbers, such as poly(ethylene-co-propylene-co-5-methylene-2-norbornene), or EPDM (ethylene-propylene-diene terpolymer) rubbers, such as Vistalon 6505 (obtained from Exxon Mobil in Houston, Texas) and its graft copolymers, have also been found to be particularly useful.

[0078] Thermoplastic elastomers can be dissolved in solvents or solvent mixtures that are immiscible with the display fluid in the microcells and exhibit a lower specific gravity than the display fluid. Low surface tension solvents are preferred for the outer coating composition because they have better wetting properties on the microcell partition walls and electrophoretic fluid. Solvents or solvent mixtures with a surface tension of less than 35 dynes / cm are preferred. More preferably, a surface tension of less than 30 dynes / cm is preferred. Suitable solvents include alkanes (preferably C44). 6-12 Alkanes, such as heptane, octane or Isopar solvent from Exxon Chemical Company, nonane, decane and their isomers), cycloalkanes (preferably C44-2 ... 6-12 Cycloalkanes, such as cyclohexane and naphthane, and alkylbenzenes (preferably mono- or di-C) 1-6 Alkylbenzenes, such as toluene, xylene, etc.), alkyl esters (preferably C450) 2-5 Alkyl esters (such as ethyl acetate, isobutyl acetate, etc.) and C 3-5Alkyl alcohols (such as isopropanol and its isomers). Mixtures of alkylbenzenes and alkanes are particularly useful.

[0079] In addition to polymer additives, polymer blends may also include wetting agents (surfactants). Wetting agents such as FC surfactants from 3M, Zonyl fluorosurfactants from DuPont, fluoroacrylates, fluoromethacrylates, fluorinated long-chain alcohols, perfluorinated long-chain carboxylic acids and their derivatives, and Silwet siloxane surfactants from OSi in Greenwich, Connecticut, may also be included in the composition to improve the adhesion of the sealant to the microcells and provide a more flexible coating process. Other components, including crosslinking agents (e.g., diazidides, such as 4,4'-diazidodiphenylmethane and 2,6-di-(4'-azidobenzaldehyde)-4-methylcyclohexanone), vulcanizing agents (e.g., 2-benzothiazolyl disulfide and tetramethylthiuram disulfide), multifunctional monomers or oligomers (e.g., hexanediol, diacrylate, trimethylolpropane, triacrylate, divinylbenzene, diallyl phthalate), thermal initiators (e.g., dilauryl peroxide, benzoyl peroxide), and photoinitiators (e.g., isopropylthioxanthone (ITX), Irgacure 651 and Irgacure 369 from Ciba-Geigy), are also very useful for enhancing the physical and mechanical properties of the sealant through crosslinking or polymerization reactions during or after the topcoat process.

[0080] After fabricating the microunits, they are filled with a suitable electrophoretic medium. The microunit array 640 can be prepared by any of the methods described above. Figures 6A-6D As shown in the cross-section, microcell partition walls 661 extend upward from substrate 663 to form open cells. The microcells may include a primer layer 662 to passivate the mixture and prevent the microcell material from interacting with the mixture containing electrophoretic medium 665.

[0081] Next, the microunits are filled with an electrophoretic medium 664, which contains particles 665 in a nonpolar fluid. Various techniques can be used to fill the microunits. In some instances, microunits can be filled to the depth of the microunit separator walls 661 using a blade coating technique. In other instances, microunits can be filled using inkjet microinjection. In still other instances, an array of microneedles can be used to fill the microunit array.

[0082] like Figure 6CAs shown, after filling, the microcells are sealed by applying polymer 1466, which serves as a sealing layer. In some instances, the sealing process may involve exposure to heat, dry hot air, or UV radiation. Polymer 666 is compatible with the electrophoretic medium but is not fluidized by the electrophoretic medium 664. Therefore, the final microcell structure is mostly leak-proof and can withstand bending without delamination.

[0083] By employing iterative photolithography, various individual microcells can be filled with a desired electrophoretic medium. The process typically involves coating an empty microcell array with a layer of positive working photoresist, selectively opening a number of microcells by image-based exposure of the positive photoresist, developing the photoresist, filling the open microcells with a desired mixture, and sealing the filled microcells through a sealing process.

[0084] After the microcells 660 are filled, the sealed array can be laminated with a finishing layer 668, preferably by pre-coating the finishing layer 668 with an adhesive layer, which can be a pressure-sensitive adhesive, a hot melt adhesive, or a thermosetting, moisture-curing, or radiation-curing adhesive. If the top conductor film is transparent to radiation, the laminated adhesive can be post-cured by radiation such as UV through the top conductor film.

[0085] 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 comprise an organic pigment. The shell comprises a polymer that is in contact with the pigment surface of the core. The polymer of 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 organic pigment surface of the core. Core-shell first-type particles can be formed by dispersion polymerization. In one example, dispersion polymerization is a free radical polymerization of one or more monomers in the presence of pigment particles. If core-shell particles are prepared by dispersion polymerization, the polymer of the shell is adsorbed onto the pigment surface of the core.

[0086] Vinylnaphthalene can be 1-naphthalene, 2-naphthalene, 1-naphthalene having one or more substituents on the aromatic carbon of vinylnaphthalene, or 2-naphthalene having one or more substituents on the aromatic carbon of vinylnaphthalene.

[0087] Vinylnaphthalene can 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.

[0088] 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.

[0089] Vinylnaphthalene may have alkyl substituents. 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.

[0090] Other non-limiting examples of substituted 1-vinylnaphthalene and 2-vinylnaphthalene include 2-nitro-1-vinylnaphthalene, methyl 6-carboxylate-2-vinylnaphthalene, 6-hydroxy-2-vinylnaphthalene, 1-(2-fluorophenyl)-2-vinylnaphthalene, and 2,7-bis(vinyl)naphthalene.

[0091] The shell of the first type of particle may contain a copolymer. The copolymer can be formed by reacting vinylnaphthalene with a first monomer. The first monomer may be a macromolecular monomer.

[0092] Non-limiting examples of the first monomer include styrene, α-methylstyrene, methyl acrylate, methyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, vinylpyridine, n-vinylpyrrolidone, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, hexyl acrylate, hexyl methacrylate, n-octyl acrylate, n-octyl methacrylate Octadecyl acrylate, octadecyl methacrylate, 2-perfluorobutyl ethyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, and 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, etc.

[0093] Macromonomers may contain terminal functional groups selected from acrylate groups, methacrylate groups, vinyl groups, or combinations thereof.

[0094] Examples of macromonomers that can be used to form the first type of particles are described in U.S. Patent Application No. 2018 / 0210312, the contents of which are incorporated herein by reference in their entirety. One type of macromonomer that can be used to form the shell of a core-shell particle includes acrylate-terminated polysiloxanes, such as 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.

[0095] Another type of macromonomer suitable for this method is the PE-PEO macromonomer, as shown below:

[0096] R m O-[-CH2CH2O-] n -CH2-phenyl-CH=CH2; or

[0097] R m O-[-CH2CH2O-] n -C(=O)-C(CH3)=CH2.

[0098] The substituent R can be a polyethylene chain, n is 1-60, and m is 1-500. Synthesies of these compounds can be found in Dongri Chao et al., Polymer Journal, Vol. 23, no. 9, 1045 (1991) and Koichi Ito et al., Macromolecules, 1991, 24, 23488. Another suitable type of macromonomer is the PE macromonomer, as shown below:

[0099] CH3-[-CH2-] n -CH2O-C(=O)-C(CH3)=CH2.

[0100] In this case, n is 30-100. The synthesis of this type of macromonomer can be found in Seigou Kawaguchi et al, Designed Monomers and Polymers, 2000, 3, 263.

[0101] The first monomer may be selected from methyl methacrylate, lauryl methacrylate, 2,2,2-trifluoroethyl methacrylate, acrylate-terminated polysiloxanes, and methacrylate-terminated polysiloxanes.

[0102] The copolymer can be formed from vinylnaphthalene, a first monomer, and a second monomer. The copolymer can be formed from vinylnaphthalene, 2,2,2-trifluoroethyl methacrylate, and a macromonomer whose structure includes (i) polydimethylsiloxane and (ii) vinyl, acrylate, or methacrylate functional groups. The macromonomer can be a monomethacryloyloxypropyl-terminated polydimethylsiloxane. The second monomer can be selected from monomer examples (including the macromonomer) of the first monomer described above.

[0103] The copolymer can be formed from vinylnaphthalene, a first monomer, a second monomer, and a third monomer. The third monomer can be selected from the monomer examples described above for the first monomer (including macromonomers).

[0104] The electrophoretic medium includes 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.

[0105] The electrophoretic medium can include type I particles, type II particles, type III particles, and type IV particles. Type I, II, III, and IV particles have different colors; type I, II, III, and IV particles can contain organic pigments. Type I, II, and III particles can have a charge polarity opposite to that of type IV particles. Type IV particles can contain inorganic pigments. The colors of type I, II, and III pigments can be selected from blue, red, yellow, cyan, magenta, and green. The color of type IV pigments can be white.

[0106] In one instance, the first, second, and third types of particles can be selected from blue, red, and yellow, and the fourth type of particle can be white. In this instance, the first type of particle can be yellow.

[0107] In another example, the first, second, and third types of particles can be selected from cyan, magenta, and yellow, and the fourth type of particle can be white. In this example, the first type of particle can be magenta.

[0108] The electrophoretic medium may include type I particles, type II particles, type III particles, and type IV particles. Types I, II, III, and IV particles have different colors; types I, II, and III particles may contain organic pigments. Types I and II particles may have a charge polarity opposite to that of types III and IV particles. Type IV particles may contain inorganic pigments. The colors of type I, II, and III pigments may be selected from blue, red, yellow, cyan, magenta, and green. The color of type IV pigment may be white.

[0109] The electrophoretic medium may include particles of type I, type II, type III, type IV, and type V. Particles of types I, II, III, IV, and V have different colors; particles of types I, II, and III may contain organic pigments. Particles of types I and II may have a charge polarity opposite to that of particles of types III and IV. Particles of type IV may contain inorganic pigments. The colors of pigments of types I, II, and III may be selected from cyan, magenta, and yellow. The color of pigment of type IV may be white. Particles of types I and IV may carry a negative charge, while particles of types II, III, and V may carry a positive charge. Particles of type I may have a more negative zeta potential than particles of type IV. Particles of type V may have a greater zeta potential than particles of types II and III. Particles of types IV and V may be selected from white and black. In one example, the electrophoretic medium of the present invention has particles of types I, II, III, IV, and V respectively, being yellow, red, blue, white, and black. In this example, particles of types I and IV are negatively charged, and the zeta potential of particles of type I is more negative than that of particles of type IV. In the same instance, the particles of types 2, 3, and 5 are positively charged, and the particles of type 5 have a larger zeta potential than those of types 2 and 3.

[0110] Organic pigments with a nucleus of type I particles can be selected from azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, isoindoline pigments, anthrone pigments, indanone pigments, carbon black pigments, rhodamine pigments, aniline pigments, carbon black pigments, and mixtures thereof.

[0111] Organic pigments of type I, type II, and type III particles can be independently selected from CI Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6, 60, and 79; Pigment Red 2, 4, 5, 9, 12, 14, 38, 48:2, 48:3, 48:4, 52:2, 53:1, 57:1, 81, 112, 122, 144, 146, 147, 149, 168, 170, 176, 177, 179, 184, 185, 187, 188, 208, 209, 210, 214, 242, 254, 255, 257, 262, 264, 282, and 285. CI pigments: Violet 1, 19, 23 and 32; CI pigments: Yellow 1, 3, 12, 13, 14, 15, 16, 17, 73, 74, 81, 83, 97, 109, 110, 111, 120, 126, 127, 137, 138, 139, 150, 151, 154, 155, 174, 175, 176, 180, 181, 184, 191, 194, 213 and 214; CI pigments: Green 7 and 36; CI pigments: Black 1 and 7; CI pigments: Brown 25, 32, 41; Pigments: Orange 5, 13, 34, 36, 38, 43, 61, 62, 64, 68, 67, 72, 73 and 74, and mixtures thereof.

[0112] The electrophoretic medium of the present invention can be manufactured by a method comprising the following steps: (a) providing a dispersion containing 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 particles of a first type; (c) washing the particles of the first type 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 include the step of adding a charge control agent to the dispersion of washed particles in the nonpolar liquid.

[0113] The organic pigments of the core of the first type of particles 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.

[0114] Organic pigments provide color because they absorb incident light at specific wavelengths corresponding to visible light. Typically, their color saturation and intensity increase with decreasing particle size (i.e., with increasing surface area). Therefore, they mostly exist as particles with relatively high surface area, making them relatively difficult to disperse and stabilize in liquids.

[0115] The electrophoretic medium of the present invention can comprise multiple particles of first, second, third, and fourth types. First-type particles comprise a core and a shell. The core comprises an organic pigment, and the shell comprises a polymer. Second-type particles can also comprise a core and a shell, wherein the core comprises an organic pigment, and the shell comprises a polymer. Third-type particles can also comprise a core and a shell, wherein the core comprises an organic pigment, and the shell comprises a polymer. Fourth-type particles can also comprise a core and a shell, wherein the core comprises an organic pigment, and the shell comprises a polymer. Fourth-type particles can include a core and a shell, wherein the core comprises an inorganic pigment, and the shell comprises a polymer.

[0116] To produce the first type of particles, the amounts of reagents used (e.g., organic pigments, vinylnaphthalene, 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 type of polymerization.

[0117] The first type of particles prepared according to various embodiments of the invention are dispersed in a nonpolar liquid. It is desirable that the polymer layer is compatible with the nonpolar liquid. In practice, the nonpolar liquid suspended in the electrophoretic medium is typically hydrocarbon-based, although the nonpolar liquid may include a proportion of halogenated hydrocarbons to increase the density of the nonpolar liquid and thus reduce the difference between the density of the nonpolar liquid and the density of the particles. Therefore, the polymer of the shell may include hydrocarbon chains compatible with the nonpolar liquid of the electrophoretic medium, thereby improving the dispersion stability of the particles. In one example of the first type of particles, the polymer of the shell may have a branched or "comb-like" structure, having a main chain and multiple side chains extending from the main chain. Each of these side chains may have four, five, six, or more carbon atoms. The side chains themselves may be branched; for example, each side chain may be a branched alkyl group, such as a 2-ethylhexyl group.

[0118] There are two basic methods for forming such comb-like polymers. The first method uses monomers, which themselves provide the necessary side chains. Typically, such monomers have a single polymerizable group (at least four, preferably at least six carbon atoms) at one end of a long chain. This type of monomer has been found to work well 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 may be necessary to limit the number of side chains formed in such a method, which can be achieved by using a mixture of monomers (e.g., a mixture of lauryl methacrylate and methyl methacrylate) to form a random copolymer, where only some repeating units have long side chains. In the second method, exemplified by the RGP-ATRP process, a first polymerization reaction is carried out using a mixture of monomers, at least one of which carries an initiating group, thereby generating a first polymer containing such an initiating group. The product of the first polymerization reaction is then subjected to a second polymerization, typically under different conditions than the first polymerization, so that the initiating groups in the polymer initiate the polymerization of additional monomers on the original polymer, thereby forming the desired side chains.

[0119] Using conventional free radical initiators, such as azobisisobutyronitrile (AIBN), free radical polymerization of vinyl or similar free radical polymerizable groups attached to particles can be carried out at elevated reaction temperatures, preferably 60 to 70 °C. ATRP polymerization can be carried out using conventional metal complexes, as described in Wang, JS, et al., Macromolecules 1995, 23, 7901, and J. Am. Chem. Soc. 1995, 117, 5614, and Beers, K. et al., Macromolecules 1999, 32, 5772-5776. See also U.S. Patents 5,763,548; 5,789,487; 5,807,937; 5,945,491; 4,986,015; 6,069,205; 6,071,980; 6,111,022; 6,121,371; 6,124,411; 6,137,012; 6,153,705; 6,162,882; 6,191,225; and 6,197,883. The entire disclosure of these papers and patents is incorporated herein by reference. Currently, the preferred catalyst for ATRP is cuprous chloride in the presence of bipyridine (Bpy).

[0120] It has been found that there is an optimal range for the amount of polymer layer formed on electrophoretic particles; excessive polymer formation on the particles reduces their electrophoretic properties. This optimal range varies depending on several factors, including the density and size of the coated particles, the properties of the suspending medium in which the particles are intended to be used, and the properties of the polymer in the particle shell. For any given pair of particles, polymer, and nonpolar liquid electrophoretic medium, the optimal range is best determined empirically. However, as a general guideline, it should be noted that the higher the particle density, the lower the optimal proportion of polymer by particle weight, while the finer the particle size, the higher the optimal proportion of polymer. Generally, the polymer content of the particles can be higher than 2% by weight, higher than 4% by weight, or higher than 6% by weight.

[0121] Based on the weight of the particles, the polymer content of the particles can be 1 to 50% by weight, 2 to 30% by weight, 4 to 20% by weight, 5 to 15% by weight, 4 to 15% by weight, 6 to 15% by weight, or 8 to 12% by weight. Example

[0122] Example 1: Preparation of the yellow particles of the present invention

[0123] In a 500 mL bottle, 60.0 g of Pigment Yellow 138 (Paliotol Yellow L0962HD, 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 materials were mixed 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 raised to 75 °C under stirring and a nitrogen atmosphere. 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 purging with nitrogen for 1 hour, a solution of 0.304 g of lauroyl peroxide initiator (provided by Sigma) dissolved in 3.5 g of ethyl acetate (provided by Sigma) was added to the reactor to initiate polymerization. After 19 hours, the mixture was centrifuged at 5000 rpm for 20 minutes, and the supernatant was removed. The resulting solid was redispersed in Isopar E, the dispersion was centrifuged, and the supernatant was removed. This washing cycle was repeated twice, and the solid was vacuum dried at room temperature to produce particles. The final pigment had a polymer content of 11%; the zeta potential of the particles was -51 mV.

[0124] Example 2: Preparation and color evaluation of the electro-optic device of the present invention.

[0125] Electrophoretic media were 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. Micro-unit electro-optic devices were fabricated using these electrophoretic media. The electro-optic devices were driven to white, black, red, yellow, blue, and green states. The color of each state was measured using a colorimeter. Table 1 shows the color measurement results for Example 2 (denoted by L*a*b*). W represents white, K represents black, R represents red, Y represents yellow, B represents blue, and G represents green.

[0126] Comparative Example 3: Preparation and color evaluation of the control electro-optic device.

[0127] The process of Example 2 was repeated, but control yellow particles were used instead of the yellow particles from Example 1 for comparison of the electrophoresis medium. 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 formed by polymerization of methyl methacrylate, monomethacryloyloxypropyl-terminated polydimethylsiloxane, and 2,2,2-trifluoroethyl methacrylate. Table 2 shows the color measurement results of Comparative Example 3 (denoted by L*a*b*). W represents white, K represents black, R represents red, Y represents yellow, B represents blue, and G represents green.

[0128]

[0129]

[0130] The data comparison in Tables 1 and 2 shows that the device of the present invention has a significantly improved yellow state (b* is 64.5 vs. 37.8). In addition, the device of the present invention also shows improved red state (a* is 37.6 vs. 33.7), blue state (b* is -38.8 vs. -9.3), and green state (a* is -38.8 vs. -12.3).

[0131] Examples 4A, 4B, 4C: Preparation of a series of yellow electrophoretic particle dispersions

[0132] A series of yellow electrophoretic ionic dispersions (4A, 4B, 4C) were prepared using a variation of the general synthetic 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 determined by thermogravimetric analysis. Additionally, the polymer was extracted from the dried particles by THF, and the extract was analyzed by gel permeation chromatography to determine the weight-average molecular weight. Table 3 summarizes the polymer content (polymer weight based on the weight of the electrophoretic particles) and weight-average molecular weight of each yellow electrophoretic particle from this series.

[0133] Examples 5A, 5B, 5C: Fabrication of electro-optic devices and evaluation of afterimages.

[0134] 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 contained yellow dispersions 4A, 4B, and 4C, respectively. The afterimage of each electro-optic device was determined by switching the device to a six-color patch image (white, black, red, yellow, blue, and green), inserting and maintaining the device in the chamber of a Q-Sun xenon arc tester (provided by Q-lab) at 50°C and 35% relative humidity, removing the device from the Q-Sun chamber, cooling to room temperature, switching the electro-optic device to its white state, and measuring the white color of each patch using a spectrophotometer (CIELAB). The afterimage was determined 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 afterimage than devices with a larger Δb*. Evaluation of the afterimage can also be performed by visual inspection of the display. Compared to the reference, the device displaying a stronger yellow hue exhibits more image retention than the device displaying a weaker yellow hue. The image retention evaluation results for electro-optical devices 5A, 5B, and 5C are provided in Table 4.

[0135]

[0136]

[0137] The evaluation results in Table 4 show that the electro-optic device containing an electrophoretic medium with yellow electrophoretic particles exhibits significantly fewer afterimages. The surface of the yellow electrophoretic particles comprises polymers with a weight-average molecular weight greater than 55,000 Da.

[0138] Example 6. Preparation of magenta particles of the present invention.

[0139] The preparation of Example 1 was repeated, but Pigment Red 122 was used as the organic pigment core, wherein the shell polymer 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 (2.5 mmol monomer per gram of pigment). The particles from Example 6B contained 48% by weight of polymer (5.0 mmol monomer per gram of pigment). The particles from Example 6C contained 38% by weight of polymer (4.0 mmol monomer per gram of pigment). The polymer content, weight-average molecular weight (MW), particle size, and zeta potential of each example were determined as shown in Table 5.

[0140]

[0141] Example 7. Preparation and stability evaluation of the electro-optic device of the present invention.

[0142] 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, which is surface-treated from a polymer formed by the polymerization of methyl methacrylate and monomethacrylate-terminated poly(dimethylsiloxane); the polymer content is 25% by weight of the particles), negatively charged white particles (as described in Example 1 of U.S. Patent No. 8,582,196), and a charge control agent CCA-111 (a cationic charge control agent of CCA111 from Example 1 of patent application US2020 / 0355978). Micro-unit electro-optic devices were fabricated using the electrophoretic medium. The electro-optic devices were driven to a white state, and the color was measured immediately (t0) and after 24 hours (t24) using a colorimeter, and reported as DE (color difference from t0 to t24 in CIELAB).

[0143] Comparative Example 8. Comparison of the fabrication and stability evaluation of electro-optic devices.

[0144] The process of Example 7 was repeated, but instead of the magenta particles from Example 6A, control magenta particles were used for the comparison electrophoresis medium. The control magenta particles 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 graft polymerization with methyl methacrylate (as described in Example 1 of U.S. Patent No. 9,697,778). Micro-unit electro-optic devices were fabricated using the electrophoresis medium. The electro-optic devices were driven to a white state, and the color was measured immediately (t0) and after 24 hours (t24) using a colorimeter, and reported as DE (color difference from t0 to t24 in CIELAB).

[0145] White state stability evaluation of Examples 7 and 8. As shown in Table 6, the white state of the device of the present invention in Example 7 was found to be more stable than that of the device in Example 8 after 24 hours. Specifically, in the white state of the device in Comparative Example 8, the color change from t0 to t24, expressed as DE, was significantly greater than the color change of the device in Example 6 of the present invention. The white state of the device in Comparative Example 8 transformed into a state with a reddish hue within 24 hours.

[0146]

[0147] The evaluation results of the above embodiments and comparative examples of the present invention show that, in terms of image quality and stability, the electro-optic device containing the electrophoretic medium of the present invention has significantly improved electro-optic performance compared with the control electrophoretic medium.

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 contains a pigment having a surface, the pigment being either an organic or inorganic pigment. The shell contains a polymer, which is a homopolymer or copolymer, the homopolymer being formed by the polymerization of vinyl naphthalene, the copolymer being formed by the polymerization of vinyl naphthalene and a first monomer, the homopolymer or copolymer being in contact with the surface of the pigment.

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

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

4. The electrophoretic medium of claim 3, wherein the one or more substituents are selected from halogens, alkoxy groups, alkyl groups, nitro groups, carboxyl groups, hydroxy groups, sulfonic acid groups, sulfonate groups, and amino groups.

5. The electrophoretic medium according to any one of claims 1 to 4, wherein the first monomer has a molecular structure, the molecular structure of the first monomer comprising functional groups selected from vinyl groups, acrylate groups and methacrylate groups.

6. The electrophoretic medium according to any one of claims 1 to 5, wherein the first monomer is a macromonomer, the macromonomer having 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 a vinyl group, a methacrylate group, or an acrylate group.

7. The electrophoretic medium according to any one of claims 1 to 6, wherein the first monomer is selected from 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 according to any one of claims 1 to 7, 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 comprising (i) polydimethylsiloxane and (ii) vinyl functional groups, acrylate functional groups or methacrylate 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 according to claim 8 or claim 9, wherein the second monomer is a monomethacryloyloxypropyl-terminated polydimethylsiloxane.

11. The electrophoretic medium according to any one of claims 1 to 10, further comprising 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 comprises an organic pigment, each of the second-type and third-type particles comprises an organic pigment, and each of the plurality of fourth-type particles comprises an inorganic pigment.

13. The electrophoretic medium according to claim 11 or claim 12, 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 according to claim 11 or claim 12, 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 the first charge polarity is opposite to the second charge polarity.

15. The electrophoretic medium according to any one of claims 11 to 14, wherein the colors of the first, second, and third types of particles are independently selected from cyan, magenta, yellow, blue, green, and red, and wherein the color of the fourth type of particles is white.

16. The electrophoretic medium according to any one of claims 11 to 15, wherein the particles of the first, second, and third types are independently selected from azo pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, isoindoline pigments, anthrone pigments, indanone pigments, rhodamine pigments, aniline pigments, carbon black pigments, and mixtures thereof.

17. An electro-optic device comprising a first transparent electrode layer, an electro-optic material layer comprising an electrophoretic medium according to 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 microunits, each of the plurality of microcapsules or each of the plurality of microunits 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 manufacturing method comprising the following steps: A first dispersion is provided, which contains an organic pigment in a first organic solvent; Vinylina, a first monomer, and a free radical initiator are added to the first dispersion to form particles of the first type; The first type of particles were washed with a second organic solvent; and The washed particles are dispersed in a nonpolar liquid.

19. The method for manufacturing the electrophoretic medium according to claim 18, wherein the first dispersion further comprises a charge control agent.

20. The method for manufacturing the electrophoretic medium according to claim 18, further comprising adding a charge control agent to the dispersion of the washed particles in the nonpolar liquid.

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