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An encapsulation material, intended for use in encapsulated electrophoretic displays, comprises the coacervation product of a polyanionic polymer having a vinyl main chain and a plurality of anionic groups bonded to the main chain, with a cationic or zwitterionic water-soluble polymer capable of for

An encapsulation material, intended for use in encapsulated electrophoretic displays, comprises the coacervation product of a polyanionic polymer having a vinyl main chain and a plurality of anionic groups bonded to the main chain, with a cationic or zwitterionic water-soluble polymer capable of forming an immiscible second phase on contact with the polyanionic polymer.

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What is claimed is: 1. A process for encapsulating a internal phase, which process comprises contacting the internal phase with a polyanionic polymer having a vinyl main chain and a plurality of anionic groups bonded to the main chain and with a cationic or zwitterionic water-soluble polymer capabl

What is claimed is: 1. A process for encapsulating a internal phase, which process comprises contacting the internal phase with a polyanionic polymer having a vinyl main chain and a plurality of anionic groups bonded to the main chain and with a cationic or zwitterionic water-soluble polymer capable of forming an immiscible second phase on contact with the polyanionic polymer, the contact being effected under conditions effective to cause formation around the internal phase of a capsule wall comprising a coacervation product of the two polymers. 2. A process according to claim 1 wherein the capsule wall formed is thereafter contacted with an aldehyde. 3. A process according to claim 2 wherein the aldehyde comprises glutaraldehyde. 4. A process according to claim 1 wherein the protein comprises gelatin. 5. A process according to claim 1 wherein the anionic groups are any one or more of sulfate, sulfonate, phosphate, carboxylic acid and carboxylate groups. 6. A process according to claim 1 wherein the polyanionic polymer is of the formula: where x and y are the mole fractions of the two monomer residues in the polymer and total 1, one or more of R1 to R8 is an anionic group, and those of R1 to R8 which are not anionic groups are hydrogen, saturated hydrocarbon groups, groups of the formula--OR9 or--COOR10 (wherein R9 and R10 are hydrocarbon groups), aryl, substituted aryl or halocarbon groups. 7. A process according to claim 1 wherein the polyanionic polymer comprises any one or more of poly(acrylic acid); poly(methacrylic acid); copolymers of poly(acrylic acid) and/or poly(methacrylic acid) with esters of the same acids; styrene sulfonate copolymers with styrene; methyl vinyl ether or vinyl acetate copolymers with (meth)acrylic acid; copolymers of alkyl-substituted olefins, methyl vinyl ether and vinyl carboxylate with maleic acid, maleic esters, and maleic half ester, half acids. 8. A process for forming a capsule, the process comprising: providing a liquid internal phase comprising a fluid and a first prepolymer dispersed therein and having a plurality of first reactive groups; providing a dispersion medium substantially immiscible with the internal phase and comprising a dispersing liquid and a second prepolymer dispersed therein and having a plurality of second reactive groups, each of the second reactive groups being capable of reacting with at least one of the first reactive groups; and dispersing the internal phase as a plurality of discrete droplets in the dispersion medium, thereby causing the first and second reactive groups to react together to form a polymer shell surrounding the droplets, and thereby forming capsules comprising the fluid. 9. A process according to claim 8 in which the internal phase further comprises a plurality of electrically charged particles capable of moving through the internal phase upon application of an electric field thereto. 10. A process according to claim 8 in which the dispersion medium is an aqueous medium and the internal phase is an organic medium. 11. A process according to claim 8 in which one of the first and second reactive groups comprises an acid anhydride grouping and the other comprises an amine group, whereby the first and second reactive groups react together to form amide linkages. 12. A process according to claim 8 in which one of the first and second prepolymers comprises poly(isoprene-graft-maleic anhydride) and the other comprises polyethyleneimine.