Particles for electrophoretic displays

1. Particles consisting of organic or inorganic pigment core particles encapsulated by a porous polymeric shell consisting of monomer units of at least one polymerisable steric stabiliser, at least one co-monomer, optionally at least one polymerisable dye, wherein the particles have a density of ≦2.0 g/ml and wherein pores in the polymeric shell of the particles are at least partially filled with a polar organic solvent, and wherein the particles are formed from a dispersion comprising 0.1-80% by weight of at least one organic or inorganic pigment particle, 0.1-50% by weight of at least one polar organic solvent, 0.1-50% by weight of at least one polymerisable steric stabiliser, and 40-95% by weight of co-monomer based on the total weight of the dispersion except solvent.

2. The particles according to claim 1 , wherein the polymerisable steric stabiliser is a poly(dimethylsiloxane) macromonomer with at least one polymerisable group and a molecular weight in the range of 1000-50000.

3. The particles according to claim 1 , wherein the polymerisable steric stabiliser is a mono-methacrylate terminated poly-dimethylsiloxanes.

4. The particles according to claim 1 , wherein the pigment core particle is titanium dioxide in the rutile, anatase, or amorphous modification or carbon black.

5. The particles according to claim 1 , wherein the porous polymeric shell is linked to the surface of the organic or inorganic pigment core particles by at least one reagent for controlled radical polymerisation.

6. The particles according to claim 1 , wherein the particles have a diameter of 400-1000 nm.

7. A process for the preparation of particles according to claim 1 comprising

a) dispersing at least one organic or inorganic pigment particle in a solution of at least one polymerisable steric stabiliser in a non-polar organic solvent;

b) adding at least on co-monomer, at least one porogen, wherein the at least one porogen is a polar organic solvent, optionally at least one polymerisable dye, at least one initiator, and optionally at least one chain transfer agent;

c) subjecting the dispersion of step b) to heating and sonication for polymerisation,

d) optionally washing by repeated centrifugation and redispersion in fresh solvent, and

e) optionally isolating the resulting coated particles.

8. A method comprising utilizing the particles prepared by a process according to claim 7 in optical, electrooptical, electronic, electrochemical, electrophotographic, electrowetting and electrophoretic displays and/or devices, and in security, cosmetic, decorative, and diagnostic applications.

9. An electrophoretic fluid comprising particles prepared by a process according to claim 7 .

10. The process for the preparation of particles according to claim 7 , wherein the dispersion comprises 10-40% by weight of at least one porogen.

11. A method comprising utilizing the particles according to claim 1 in optical, electrooptical, electronic, electrochemical, electrophotographic, electrowetting and electrophoretic displays and/or devices, and in security, cosmetic, decorative, and diagnostic applications.

12. An electrophoretic fluid comprising particles according to claim 1 .

13. An electrophoretic display device comprising an electrophoretic fluid according to claim 12 .

14. An electrophoretic display device according to claim 13 , wherein the electrophoretic fluid is applied by a technique selected from inkjet printing, slot die spraying, nozzle spraying, and flexographic printing, or any other contact or contactless printing or deposition technique.

15. The particles according to claim 1 , wherein the polar organic solvent is selected from the group consisting of dimethyl sulfoxide, dimethylformamide, methanol, ethanol, acetonitrile and mixtures thereof.