Electrophoretic media and processes for the production thereof

• US 7,230,750 B2
• Filed: 10/07/2004
• Issued: 06/12/2007
• Est. Priority Date: 05/15/2001
• Status: Expired due to Term

• Current Assignee: E Ink Corporation (E Ink Holdings Incorporated)
• Original Assignee: E Ink Corporation (E Ink Holdings Incorporated)
• Inventors: Whitesides, Thomas H., Wilcox, Russell J., Zhou, Qingye
• Primary Examiner(s): Mack; Ricky
• Assistant Examiner(s): CHOI, WILLIAM C
• Application Number:
  US10/711,829
• Publication Number:
  US 20050168799A1
• Time in Patent Office: 978 Days
• Field of Search: 359/296, 359/321, 345/107, 106/493, 106/499, 106/502, 106/504, 428/402, 428/403, 428/405
• US Class Current: 359/296
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01P 2002/88 by thermal analysis data, e.g. TGA, DTA, DSC
• CPC Class Codes: C01P 2004/32 Spheres
• CPC Class Codes: C01P 2004/51 Particles with a specific particle size distribution
• CPC Class Codes: C01P 2004/61 Micrometer sized, i.e. from 1-100 micrometer
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2004/82 two phases having the same anion, e.g. both oxidic phases
• CPC Class Codes: C01P 2004/84 one phase coated with the other
• CPC Class Codes: C01P 2006/10 Solid density
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: C01P 2006/60 Optical properties, e.g. expressed in CIELAB-values
• CPC Class Codes: C01P 2006/80 Compositional purity
• CPC Class Codes: C01P 2006/90 Other properties not specified above
• CPC Class Codes: C09B 67/0013 with polymeric coatings
• CPC Class Codes: C09B 68/41 Polymers attached to the pigment surface C09B68/444, C09B68/446 take precedence
• CPC Class Codes: C09B 68/44 Non-ionic groups, e.g. halogen, OH or SH
• CPC Class Codes: C09C 1/00 Treatment of specific inorganic materials other than fibrous fillers tenebrescent materials C09K9/00; luminescent materials C09K11/00; Preparation of carbon black
• CPC Class Codes: C09C 1/24 Oxides of iron
• CPC Class Codes: C09C 1/343 containing silicon or associated with silicon containing material, except when silicon only occurs in a thin coating of the particles
• CPC Class Codes: C09C 3/10 : Treatment with macromolecular organic compounds C09C3/006 takes precedence
• CPC Class Codes: G01N 27/44747 : Composition of gel or of carrier mixture
• CPC Class Codes: G02F 1/167 : by electrophoresis
• CPC Class Codes: G02F 2001/1678 : characterised by the composition or particle type
• CPC Class Codes: G02F 2202/022 : polymeric
• CPC Class Codes: Y10T 428/2991 : Coated

Abstract

A first electrophoretic medium comprises an electrically charged particle suspended in a suspending fluid, the particle having a polymeric shell having repeating units derived from at least one monomer the homopolymer of which is incompatible with the suspending fluid. A second, similar electrophoretic medium comprises a suspending fluid, and first and second types of electrically charged particle suspended in the suspending fluid, the two types of particle having differing optical characteristics but both having polymeric shells. The polymeric shells are arranged such that homoaggregation of the two types of particles is thermodynamically favored over heteroaggregation.

Claims

1. An electrophoretic medium comprising a first electrically charged particle suspended in a suspending fluid, the first particle having a polymeric shell having repeating units derived from at least one monomer the homopolymer of which is incompatible with the suspending fluid, the electrophoretic medium further comprising a second electrically charged particle having at least one optical property differing from that of the first electrically charged particle, the second electrically charged particle having a polymeric shell.

2. An electrophoretic medium according to claim 1 wherein the polymeric shell of the first particle further comprises repeating units derived from at least one monomer the homopolymer of which is compatible with the suspending fluid.

3. An electrophoretic medium according to claim 2 wherein the at least one monomer forming the compatible homopolymer comprises from about 15 to about 99 per cent by weight of the polymer shell of the first particle.

4. An electrophoretic medium according to claim 3 wherein the at least one monomer forming the compatible homopolymer comprises from about 50 to about 99 per cent by weight of the polymer shell of the first particle.

5. An electrophoretic medium according to claim 2 wherein the monomer forming the compatible homopolymer comprises lauryl methacrylate and the monomer forming the incompatible homopolymer comprises any one or more or styrene, t-butyl methacrylate and N-vinylpyrrolidone.

6. An electrophoretic medium according to claim 1 wherein the suspending fluid comprises a hydrocarbon.

7. An electrophoretic medium according to claim 1 wherein the monomer forming the incompatible homopolymer comprises any one of more of acrylates and methacrylates formed from alcohols containing not more than about eight carbon atoms, said alcohols optionally containing hydroxyl or fluoro substituents;

acrylamides and methacrylamides;

N,N-dialkylacrylamides;

N-vinylpyrrolidone;

styrene and derivatives thereof vinyl esters;

vinyl halides;

polyfluoroaromatic molecules containing a polymerizable functional group; and

silicone-containing molecules containing a polymerizable functional group.

8. An electrophoretic medium according to claim 7 wherein the monomer forming the incompatible homopolymer comprises any one of more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, trifluoroethyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, acrylamide, acrylic acid, acrylonitrile, methyl vinyl ketone, methacrylamide, N-vinylpyrrolidone, styrene, vinyl acetate, vinyl chloride, vinylidene chloride, and pentafluorostyrene.

9. An electrophoretic medium according to claim 1 wherein the first particle comprises titania and the second particle comprises carbon black or copper chromite.

10. An electrophoretic medium comprising:

a suspending fluid;

a plurality of first electrically charged particles suspended in the suspending fluid, the first electrically charged particles having a polymeric shell; and

a plurality of second electrically charged particles suspended in the suspending fluid, the second electrically charged particles having an optical property differing from that of the first electrically charged particles, and a polymeric shell;

wherein the polymeric shells are arranged such that homoaggregation of the first and second particles is thermodynamically favored over heteroaggregation.

11. An electrophoretic medium according to claim 10 wherein the polymeric shells of the first and second particles each comprise repeating units derived from at least one monomer the homopolymer of which is incompatible with the suspending fluid.

12. An electrophoretic medium according to claim 11 wherein each polymeric shell further comprises repeating units derived from at least one monomer the homopolymer of which is compatible with the suspending fluid.

13. An electrophoretic medium according to claim 12 wherein the at least one monomer forming the compatible homopolymer comprises from about 15 to about 99 per cent by weight of the polymer shell.

14. An electrophoretic medium according to claim 13 wherein the at least one monomer forming the compatible homopolymer comprises from about 50 to about 99 per cent by weight of the polymer shell.

15. An electrophoretic medium according to claim 12 wherein the monomer forming the compatible homopolymer comprises lauryl methacrylate and the monomer forming the incompatible homopolymer comprises any one or more or styrene, t-butyl methacrylate and N-vinylpyrrolidone.

16. An electrophoretic medium according to claim 11 wherein the monomer forming the incompatible homopolymer comprises any one of more of acrylates and methacrylates formed from alcohols containing not more than about eight carbon atoms, said alcohols optionally containing hydroxyl or fluoro substituents;

acrylamides and methacrylamides;

N,N-dialkylacrylamides;

N-vinylpyrrolidone;

styrene and derivatives thereof vinyl esters;

vinyl halides;

polyfluoroaromatic molecules containing a polymerizable functional group; and

silicone-containing molecules containing a polymerizable functional group.

17. An electrophoretic medium according to claim 16 wherein the monomer forming the incompatible homopolymer comprises any one of more of methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, trifluoroethyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, acrylamide, acrylic acid, acrylonitrile, methyl vinyl ketone, methacrylamide, N-vinylpyrrolidone, styrene, vinyl acetate, vinyl chloride, vinylidene chloride, and pentafluorostyrene.

18. An electrophoretic medium according to claim 10 wherein the suspending fluid has a dielectric constant less than about 5.

19. An electrophoretic medium according to claim 10 wherein the suspending fluid comprises a hydrocarbon.

20. An electrophoretic medium according to claim 19 wherein the suspending fluid comprises an aliphatic hydrocarbon.

21. An electrophoretic medium according to claim 19 wherein the suspending fluid comprises an aryl-alkane or dodecylbenzene.

22. An electrophoretic medium according to claim 10 having an operating voltage threshold.

23. An electrophoretic medium according to claim 10 wherein the suspending fluid and the particles are retained within a plurality of capsules or cells.

24. An electrophoretic display comprising an electrophoretic medium according to claim 10 and at least one electrode disposed adjacent the electrophoretic medium and arranged to apply an electric field thereto.

25. An electrophoretic medium according to claim 10 wherein the first electrically charged particles comprise titania and the second electrically charged particles comprise carbon black or copper chromite.