Particles for electrophoretic displays

1. Particles comprising pigment core particles encapsulated by a polymer consisting of monomer units of

a) at least one polymerisable dye,

b) at least one co-monomer,

c) at least one polymerisable steric stabiliser,

d) optionally at least one charged co-monomer, and

e) optionally at least one crosslinking co-monomer,

wherein the core particles are white reflective particles having a refractive index of ≧1.8,

wherein a single pigment core particle is coated with at least one surfactant and encapsulated by a polymer, and

wherein the pigment core particle is selected from the group consisting of titanium dioxide, zinc oxide, silicon dioxide, alumina, barium sulphate, zirconium dioxide, calcium carbonate, kaolinite, diantimony trioxide and tin dioxide.

2. The particles according to claim 1 , wherein the least one surfactant is soluble in non-polar organic solvents.

3. The particles according to claim 2 , wherein the pigment core particle is titanium dioxide in the rutile, anatase, or amorphous modification.

4. The particles according to claim 1 , wherein the at least one polymerisable dye is selected from the group consisting of azo dyes, metallised dyes, anthraquinone dyes, phthalocyanine dyes, benzodifuranones dyes, Brilliant Blue derivatives, pyrroline dyes, squarilium dyes, triphendioxazine dyes, and mixtures of these dyes.

5. The particles according to claim 1 , wherein the at least one polymerisable dye is at least one dye of Formula (VII)

wherein

X 1 , X 2 , and X 3 are independently of one another hydrogen or an electron-withdrawing group;

R 1 is hydrogen or OR′ with R′ is a linear, branched or cyclic alkyl group;

R 2 is a linear, branched or cyclic alkyl group;

R 3 and R 4 are independently of one another groups of the structure L 3 -Y 3 , L 4 -Y 4 ;

L 3 , and L 4 are linker groups and independently of one another linear or branched, substituted or unsubstituted alkylene groups where one or more non-adjacent carbon atoms may be replaced by O, S and/or N;

Y 3 , and Y 4 are independently of one another polymerisable groups;

wherein at least one of R 3 and R 4 comprises a polymerisable group and at least one of X 1 , X 2 , and X 3 is an electron-withdrawing group.

6. 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.

7. The particles according to claim 1 , wherein the polymerisable steric stabiliser is a methacryloyloxypropyl terminated polydimethylsiloxanes.

8. The particles according to claim 1 , wherein the percentage of polymerisable steric stabiliser is at least 5% by weight based on the weight of the polymer particle.

9. The particles polymer particles according to claim 1 , wherein the particles are coloured and wherein the polymer particles have a diameter of 400-1000 nm.

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

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

b) adding at least one polymerisable dye, at least one co-monomer, at least one initiator, and optionally at least one chain transfer agent;

c) subjecting the dispersion of step b) to heating and optional sonication, milling, stirring or high shear mixing for polymerisation,

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

e) optionally isolating the resulting coated particles.

11. The process according to claim 10 , wherein at least one surfactant is used in step a).

12. An electrophoretic fluid comprising particles prepared by the process of claim 10 .

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

14. The 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 contact or contactless printing or deposition technique.

15. 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.

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

17. An electrophoretic display device comprising an electrophoretic fluid according to claim 16 .