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In electrophoretic media, it is advantageous to use pigment particles having about 1 to 15 percent by weight of a polymer chemically bonded to, or cross-linked around, the pigment particles. The polymer desirably has a branched chain structure with side chains extending from a main chain. Charged or

In electrophoretic media, it is advantageous to use pigment particles having about 1 to 15 percent by weight of a polymer chemically bonded to, or cross-linked around, the pigment particles. The polymer desirably has a branched chain structure with side chains extending from a main chain. Charged or chargeable groups can be incorporated into the polymer or can be bonded to the particles separately from the polymer. The polymer-coated particles can be prepared by first attaching a polymerizable or polymerization-initiating group to the particle and then reacting the particle with one or more polymerizable monomers or oligomers.

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1. An electrophoretic medium comprising a plurality of pigment particles suspended in a suspending fluid, the pigment particles having from about 1 to about 15 percent by weight of the pigment of a polymer chemically bonded to, or cross-linked around, the pigment particles. 2. An electrophoretic med

1. An electrophoretic medium comprising a plurality of pigment particles suspended in a suspending fluid, the pigment particles having from about 1 to about 15 percent by weight of the pigment of a polymer chemically bonded to, or cross-linked around, the pigment particles. 2. An electrophoretic medium according to claim 1 wherein the polymer is cross-linked around the pigment particles. 3. An electrophoretic medium according to claim 1 wherein the polymer is chemically bonded to the pigment particles. 4. An electrophoretic medium according to claim 1 wherein the particles have from about 4 to about 15 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 5. An electrophoretic medium according to claim 4 wherein the particles have from about 6 to about 15 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 6. An electrophoretic medium according to claim 5 wherein the particles have from about 8 to about 12 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 7. An electrophoretic medium according to claim 1 wherein the particles comprise a metal oxide or hydroxide. 8. An electrophoretic medium according to claim 7 wherein the particles comprise titania. 9. An electrophoretic medium according to claim 8 wherein the titania particles have from about 6 to about 15 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 10. An electrophoretic medium according to claim 8 wherein the titania particles have from about 8 to about 12 percent by weight of the pigment of the polymer chemically bonded to the particles. 11. An electrophoretic medium according to claim 1 wherein the particles comprise carbon black. 12. An electrophoretic medium according to claim 11 wherein the carbon black particles have from about 8 to about 12 percent by weight of the carbon black of the polymer chemically bonded to the particles. 13. An electrophoretic medium according to claim 1 wherein the polymer comprises charged or chargeable groups. 14. An electrophoretic medium according to claim 13 wherein the polymer comprises amino or carboxylic acid groups. 15. An electrophoretic medium according to claim 1 wherein charged or chargeable groups are bonded to the pigment particles separately from the polymer. 16. An electrophoretic medium according to claim 1 wherein the polymer comprises a main chain and a plurality of side chains extending from the main chain, each of the side chains comprising at least about four carbon atoms. 17. An electrophoretic medium according to claim 1 wherein the polymer is formed from any one or more of an acrylate, a methacrylate and a substituted styrene. 18. An electrophoretic medium according to claim 17 wherein the polymer is formed from any one or more of 2-ethylhexyl methacrylate, methyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, lauryl methacrylate, isobornyl methacrylate, 2-ethylhexyl acrylate, t-butyl acrylate, 2,2,3,4,4,4-hexafluorylbutyl acrylate and p-chloromethylstyrene. 19. An electrophoretic medium according to claim 1 having two types of particles differing in at least one optical characteristic and having differing electrophoretic mobilities. 20. An electrophoretic medium according to claim 19 wherein both types of particles have from about 1 to about 15 percent by weight of the pigment of the polymer chemically bonded to, or cross-linked around, the pigment particles. 21. An electrophoretic medium according to claim 19 wherein the two types of particles bear charges of opposite polarity. 22. An electrophoretic medium according to claim 19 wherein the two types of particles bear charges of the same polarity but have different electrophoretic mobilities. 23. An electrophoretic medium according to claim 1 wherein the pigment particles and the fluid are encapsulated in a plurality of capsules. 24. An electrophoretic medium according to claim 23 havin g two types of particles differing in at least one optical characteristic and having differing electrophoretic mobilities encapsulated within each capsule. 25. An electrophoretic medium according to claim 24 wherein both types of particles have from about 1 to about 15 percent by weight of the pigment of the polymer chemically bonded to, or cross-linked around, the pigment particles. 26. An electrophoretic medium according to claim 25 wherein the two types of particles comprise titania and carbon black respectively and bear charges of opposite polarity. 27. An electrophoretic medium according to claim 23 wherein the capsules are held within a polymeric binder. 28. An electrophoretic medium according to claim 23 wherein the capsules are non-spherical. 29. An electrophoretic display comprising an electrophoretic medium according to claim 1 and at least one electrode arranged adjacent the medium and capable of applying an electric field to the medium. 30. An electrophoretic display according to claim 29 having two electrodes disposed on opposed sides of the electrophoretic medium, at least one of the electrodes being substantially transparent such that the electrophoretic medium can be viewed through the substantially transparent electrode. 31. An electrophoretic display according to claim 29 wherein the suspending fluid and particles are retained within a plurality of capsules, the capsules being retained within a solid binder, and the electrode being secured to the binder. 32. An electrophoretic medium comprising a plurality of carbon black particles suspended in a suspending fluid, said particles having from about 1 to about 25 percent by weight of the carbon black of a polymer chemically bonded to, or cross-linked around, the carbon black particles. 33. An electrophoretic medium according to claim 32 wherein the polymer is chemically bonded to the carbon black particles. 34. An electrophoretic medium according to claim 33 wherein the carbon black particles have from about 6 to about 14 percent by weight of the carbon black of the polymer chemically bonded to the carbon black particles. 35. An electrophoretic medium according to claim 32 wherein the polymer comprises charged or chargeable groups. 36. An electrophoretic medium according to claim 32 wherein charged or chargeable groups are bonded to the carbon particles separately from the polymer. 37. An electrophoretic medium according to claim 32 wherein the polymer comprises a main chain and a plurality of side chains extending from the main chain, each of the side chains comprising at least about four carbon atoms. 38. An electrophoretic medium according to claim 32 wherein the carbon particles and the fluid are encapsulated in a plurality of capsules. 39. An electrophoretic medium according to claim 38 having two types of particles differing in at least one optical characteristic and having differing electrophoretic mobilities encapsulated within each capsule. 40. An electrophoretic medium according to claim 38 wherein the capsules are non-spherical. 41. An electrophoretic display comprising an electrophoretic medium according to claim 32 and at least one electrode arranged adjacent the medium and capable of applying an electric field to the medium. 42. An electrophoretic medium comprising a plurality of pigment particles suspended in a suspending fluid, the pigment particles having from about 4 to about 15 percent by weight of the pigment of a polymer chemically bonded to, or cross-linked around, the pigment particles, the polymer comprising a main chain and a plurality of side chains extending from the main chain, each of the side chains comprising at least about four carbon atoms. 43. An electrophoretic medium according to claim 42 wherein each of the side chains comprises at least about six carbon atoms. 44. An electrophoretic medium according to claim 42 wherein the polymer is chemically bonded to the pigment particles. 45. An electrophoretic medium according to claim 42 wherein the particles have from about 6 to about 15 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 46. An electrophoretic medium according to claim 45 wherein the particles have from about 8 to about 12 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 47. An electrophoretic medium according to claim 42 wherein the particles comprise a metal oxide or hydroxide. 48. An electrophoretic medium according to claim 47 wherein the particles comprise titania. 49. An electrophoretic medium according to claim 42 wherein the particles comprise carbon black. 50. An electrophoretic medium according to claim 42 wherein the polymer comprises charged or chargeable groups. 51. An electrophoretic medium according to claim 50 wherein the polymer comprises amino or carboxylic acid groups. 52. An electrophoretic medium according to claim 42 wherein charged or chargeable groups are bonded to the pigment particles separately from the polymer. 53. An electrophoretic medium according to claim 42 wherein the polymer is formed from any one or more of an acrylate, a methacrylate and a substituted styrene. 54. An electrophoretic medium according to claim 53 wherein the polymer is formed from any one or more of 2-ethylhexyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, lauryl methacrylate, isobornyl methacrylate, 2-ethylhexyl acrylate, t-butyl acrylate, 2,2,3,4,4,4-hexafluorylbutyl acrylate and p-chloromethylstyrene. 55. An electrophoretic medium according to claim 42 having two types of particles differing in at least one optical characteristic and having differing electrophoretic mobilities. 56. An electrophoretic medium according to claim 55 wherein both types of particles have a polymer chemically bonded to, or cross-linked around, the pigment particles, the polymer comprising a main chain and a plurality of side chains extending from the main chain, each of the side chains comprising at least about four carbon atoms. 57. An electrophoretic medium according to claim 55 wherein the two types of particles bear charges of opposite polarity. 58. An electrophoretic medium according to claim 55 wherein the two types of particles bear charges of the same polarity but have different electrophoretic mobilities. 59. An electrophoretic medium according to claim 42 wherein the pigment particles and the fluid are encapsulated in a plurality of capsules. 60. An electrophoretic medium according to claim 59 having two types of particles differing in at least one optical characteristic and having differing electrophoretic mobilities encapsulated within each capsule. 61. An electrophoretic medium according to claim 60 wherein both types of particles have a polymer chemically bonded to, or cross-linked around, the pigment particles, the polymer comprising a main chain and a plurality of side chains extending from the main chain, each of the side chains comprising at least about four carbon atoms. 62. An electrophoretic medium according to claim 61 wherein the two types of particles comprise titania and carbon black respectively and bear charges of opposite polarity. 63. An electrophoretic medium according to claim 59 wherein the capsules are held within a polymeric binder. 64. An electrophoretic medium according to claim 59 wherein the capsules are non-spherical. 65. An electrophoretic display comprising an electrophoretic medium according to claim 42 and at least one electrode arranged adjacent the medium and capable of applying an electric field to the medium. 66. An electrophoretic display according to claim 65 having two electrodes disposed on opposed sides of the electrophoretic medium, at least one of the electrodes being substantially transparent such that the electrophoretic medium can be viewed through the substantially transparent electrode. 67. An electrophoretic display according to claim 65 wherein the suspending fluid and particles are retained within a p lurality of capsules, the capsules being retained within a solid binder, and the electrode being secured to the binder. 68. A two-phase electrophoretic medium comprising a continuous phase and a discontinuous phase, the continuous phase comprising at least about 40 percent by volume of the electrophoretic medium, the discontinuous phase comprising a plurality of droplets, each of which comprises a suspending fluid and at least one pigment particle disposed within the suspending fluid and capable of moving through the fluid upon application of an electric field to the electrophoretic medium, the continuous phase surrounding and encapsulating the discontinuous phase, the pigment particle comprising a polymer chemically bonded to, or cross-linked around, the pigment particle. 69. An electrophoretic medium according to claim 68 wherein the discontinuous phase comprises from about 50 to about 80 percent by volume of the electrophoretic medium. 70. A electrophoretic medium according to claim 68 wherein the continuous phase comprises a radiation-cured material. 71. An electrophoretic medium according to claim 68 wherein the continuous phase comprises gelatin. 72. An electrophoretic medium according to claim 71 wherein the gelatin comprises about 5 percent to about 15 percent by weight of the electrophoretic medium. 73. An electrophoretic medium according to claim 68 wherein the polymer is cross-linked around the pigment particles. 74. An electrophoretic medium according to claim 68 wherein the polymer is chemically bonded to the pigment particles. 75. An electrophoretic medium according to claim 68 wherein the particles have from about 1 to about 15 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 76. An electrophoretic medium according to claim 75 wherein the particles have from about 4 to about 15 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 77. An electrophoretic medium according to claim 76 wherein the particles have from about 8 to about 12 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 78. An electrophoretic medium according to claim 68 wherein the particles comprise a metal oxide or hydroxide. 79. An electrophoretic medium according to claim 78 wherein the particles comprise titania. 80. An electrophoretic medium according to claim 79 wherein the titania particles have from about 6 to about 15 percent by weight of the pigment of the polymer chemically bonded to the pigment particles. 81. An electrophoretic medium according to claim 80 wherein the titania particles have from about 8 to about 12 percent by weight of the pigment of the polymer chemically bonded to the particles. 82. An electrophoretic medium according to claim 68 wherein the particles comprise carbon black. 83. An electrophoretic medium according to claim 82 wherein the carbon black particles have from about 1 to about 25 percent by weight of the carbon black of a polymer chemically bonded to the particles. 84. An electrophoretic medium according to claim 83 wherein the carbon black particles have from about 8 to about 12 percent by weight of the carbon black of the polymer chemically bonded to the particles. 85. An electrophoretic medium according to claim 68 wherein the polymer comprises charged or chargeable groups. 86. An electrophoretic medium according to claim 85 wherein the polymer comprises amino or carboxylic acid groups. 87. An electrophoretic medium according to claim 68 wherein charged or chargeable groups are bonded to the pigment particles separately from the polymer. 88. An electrophoretic medium according to claim 68 wherein the polymer comprises a main chain and a plurality of side chains extending from the main chain, each of the side chains comprising at least about four carbon atoms. 89. An electrophoretic medium according to claim 68 wherein the polymer is formed from any one or more of an acrylate, a methacr ylate and a substituted styrene. 90. An electrophoretic medium according to claim 89 wherein the polymer is formed from any one or more of 2-ethylhexyl methacrylate, methyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, lauryl methacrylate, isobornyl methacrylate, 2-ethyhexyl acrylate, t-butyl acrylate, 2,2,3,4,4,4-hexafluorylbutyl acrylate and p-chloromethylstyrene. 91. An electrophoretic medium according to claim 68 having two types of particles differing in at least one optical characteristic and having differing electrophoretic mobilities. 92. An electrophoretic medium according to claim 91 wherein both types of particles have from about 1 to about 15 percent by weight of the pigment of the polymer chemically bonded to, or cross-linked around, the pigment particles. 93. An electrophoretic medium according to claim 91 wherein the two types of particles bear charges of opposite polarity. 94. An electrophoretic medium according to claim 91 wherein the two types of particles bear charges of the same polarity but have different electrophoretic mobilities. 95. An electrophoretic medium according to claim 91 wherein the two types of particles comprise titania and carbon black respectively and bear charges of opposite polarity. 96. An electrophoretic medium according to claim 68 wherein the droplets are non-spherical. 97. An electrophoretic display comprising an electrophoretic medium according to claim 68 and at least one electrode arranged adjacent the medium and capable of applying an electric field to the medium. 98. An electrophoretic display according to claim 68 having two electrodes disposed on opposed sides of the electrophoretic medium, at least one of the electrodes being substantially transparent such that the electrophoretic medium can be viewed through the substantially transparent electrode. 99. A pigment particle for use in an electrophoretic medium, the pigment particle having a polymer chemically bonded to, or cross-linked around, the pigment particle, the pigment particle also having a charged or chargeable group bonded to the pigment particle separately from the polymer. 100. A pigment particle according to claim 99 wherein said polymer is essentially free from charged or chargeable groups. 101. A pigment particle according to claim 99 wherein the polymer is chemically bonded to the pigment particle. 102. An electrophoretic medium comprising at least one particle according to claim 99 suspended in a suspending fluid. 103. An electrophoretic medium according to claim 102 wherein the at least one particle and the suspending fluid are encapsulated within a capsule. 104. An electrophoretic display comprising an electrophoretic medium according to claim 102 and at least one electrode arranged adjacent the medium and capable of applying an electric field to the medium.