Coloured particles for electrophoretic displays
This invention relates to colored polymer particles preferably with surface functionality for charge retention, a process for their preparation, the use of these particles for the preparation of an electrophoretic device, and to color electrophoretic displays comprising such particles.
1. A process for the preparation of colored polymer particles for use in electrophoretic devices, comprising the steps of:
a) preparing polymer particles,
b) coloring the polymer particles by addition of at least one polymerizable dye,
c) polymerizing the polymerizable dye, and optionally
d) washing and drying the colored polymer particles,
wherein the polymerizable dye is Disperse Red 1 methacrylate or acrylate, Disperse Yellow 7 methacrylate or acrylate, a dye of formula 1, a dye of Formula 2 or a dye of formula 3:
wherein R1,R2,R3,R5 and R7=alkyl,
R4, R6 and R8=H or CH 3 ,
Hal=halogen,
A − =a halogen or monobasic acid (oxo) anion.
2. The process according to claim 1 , wherein the polymerizable dye is homo-polymerized.
3. The process according to claim 1 , wherein the polymerizable dye is co-polymerised with additional monomers.
4. The process according to claim 1 , wherein an oil-soluble thermal initiator and/or a surfactant is added in step c).
5. The process according to claim 1 , wherein the polymer particles of step a) are prepared from a composition comprising a monomer, a crosslinker, an ionic monomer, and an initiator by surfactant-free emulsion copolymerisation in a batch process.
6. The process according to claim 1 , wherein the coloring of the polymer particles in step b) is done by solvent swelling with at least one polymerizable dye at a temperature range from 50-90° C.
7. The process according to claim 1 , wherein the colored polymer particles have a diameter of 50-1000 nm.
8. Colored polymer particles comprising a polymeric framework and at least one polymerized dye prepared by the process of claim 1 .
9. A mono, bi or polychromal electrophoretic device comprising colored polymer particles according to claim 8 .
10. An electrophoretic fluid comprising colored polymer particles according claim 8 .
11. An electrophoretic display device comprising colored polymer particles according to claim 8 .
12. A process according to claim 1 , wherein the polymer particles prepared in step a) comprise sites of charging and/or of stabilization.
13. A process according to claim 1 , wherein the polymerizable dye is a dye of formula 1 which is a methacrylate or acrylate ester derivative of CI Basic Blue 41, a dye of Formula 2 wherein Hal=C1 and R5 and R6=CH 3 , or a dye of formula 3 wherein R7=C 2 H 5 and R8=CH 3 .
14. A process according to claim 1 , wherein, in the formulae:
R1,R2,R3,R5, R7=C 1 -C 4 alkyl, and
A − =acetate, propionate, lactate, methane sulphonate, p-toluenesulphonate, hydroxide or nitrate anion.
15. The process according to claim 1 , wherein the colored polymer particles have a diameter of 150-600 nm.