Coloured polymer particles
This invention relates to coloured polymer particles prepared by a reverse emulsion solvent removal process, electrophoretic fluids comprising such particles, and electrophoretic display devices comprising such fluids.
1. A process for the preparation of coloured polymer particles for use in electrophoretic devices, comprising the steps of
a) forming a reverse emulsion comprising
1) at least one polymer, at least one, dye, at least one polar solvent, at least one non-polar solvent, and at least one optionally charged surfactant, or
2) at least one pre-polymerized dye at least one polar solvent, at least one non-polar solvent, and at least one optionally charged surfactant,
b) removing the polar solvent or polar solvents by evaporative methods and
c) optionally removing the non-polar solvent or non-polar solvents,
wherein the non-polar solvent used in step a) is dodecane, tetradecane, decane, nonane, or mixtures thereof.
2. The process according to claim 1 , wherein the reverse emulsion of step a) is prepared by al) forming a polar phase by mixing at least one polar solvent with at least one pre-polymerized dye or with a combination of a dye and at least one polymer, a2)forming a non-polar phase by mixing at least one non-polar solvent, and at least one surfactant, a3) combining the polar phase and the non-polar phase, and a4) homogenising the combined phases to form the reverse emulsion.
3. The process according to claim 1 , wherein the dye is water-soluble or water-dispersible.
4. The process according to claim 1 , wherein the dye comprises a chromophoric group and optional groups to modify physical properties and/or optionally charged groups and/or optionally linker groups and/or optionally polymerisable groups.
5. The process according to claim 1 , wherein amaranth, basic blue 41 methacrylate, and/or acid yellow 9 are used as dyes.
6. The process according to claim 1 , wherein the polymer of step a) is hydrophilic and/or charged.
7. The process according to claim 1 , wherein the polar solvent used in step a) is water, low molecular weight alcohol, acetonitrile, DMSO, DMF or mixtures thereof.
8. The process according to claim 1 , wherein the polar solvent used in step a) is water and/or ethanol.
9. The process according to claim 1 , wherein the non-polar solvent used in step a) has a refractive index and a density similar to that of the polymer used in step a).
10. The process according to claim 9 , wherein the non-polar solvent used in step a) is dodecane.
11. The process according to claim 1 , wherein a pre-polymerised dye, optionally co-polymerised dye, is used.
12. The process according to claim 1 , wherein the reverse emulsion additionally comprises a reflective particle.
13. The process according to claim 1 , wherein the reverse emulsion additionally comprises titanium dioxide.
14. The process according to claim 1 , wherein the coloured polymer particles are cross-linked during or post particle formation according to steps a) to c).
15. The process as claimed in claim 1 which consists of the steps a) and b).