Electrophoretic particles and processes for the production thereof

• US 7,411,720 B2
• Filed: 02/09/2007
• Issued: 08/12/2008
• Est. Priority Date: 05/15/2001
• Status: Expired due to Term

• Current Assignee: E Ink Holdings Incorporated
• Original Assignee: E Ink Holdings Incorporated
• Inventors: Paolini, Richard J. Jr., Herb, Craig A., Honeyman, Charles Howie, Zhang, Libing, King, Matthew A., Pullen, Anthony Edward, Houde, Kimberly L., Gates, Elizabeth Moran, Pratt, Emily J.
• Primary Examiner(s): Schwartz; Jordan M.
• Assistant Examiner(s): JONES, JAMES
• Application Number:
  US11/673,269
• Publication Number:
  US 20070128352A1
• Time in Patent Office: 550 Days
• Field of Search: 359/296
• 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 68/20 characterised by the process features
• CPC Class Codes: C09B 68/24 Azo-coupling
• CPC Class Codes: C09B 68/41 Polymers attached to the pigment surface C09B68/444, C09B68/446 take precedence
• CPC Class Codes: C09B 68/4235 Ammonium groups or derivatives thereof
• CPC Class Codes: C09B 68/44 Non-ionic groups, e.g. halogen, OH or SH
• CPC Class Codes: C09B 68/446 : Amines or polyamines, e.g. aminopropyl, 1,3,4,-triamino-pentyl or polyethylene imine
• 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: G02F 1/167 : by electrophoresis
• CPC Class Codes: G02F 2001/1678 : characterised by the composition or particle type

Abstract

In electrophoretic media, it is advantageous to use pigment particles having about 1 to 15 per cent by weight of a polymer chemically bonded to, or cross-linked around, the pigment particles. The polymer desirably has a branched chain structure with side chains extending from a main chain. Charged or chargeable groups can be incorporated into the polymer or can be bonded to the particles separately from the polymer. The polymer-coated particles can be prepared by first attaching a polymerizable or polymerization-initiating group to the particle and then reacting the particle with one or more polymerizable monomers or oligomers.

Claims

1. A process for coating a pigment particles with silica, the process comprising:

dispersing the pigment particles in a solution of a soluble silicate at a pH above about 8 and a temperature above about 60°

C.;

adding to the dispersion of the pigment particles both a solution of an acid and a solution of a soluble silicate while maintaining the temperature of the dispersion above about 60°

C., thereby causing deposition of silica on to the particles; and

lowering the pH of the dispersion below about 4, and thereafter separating the silica-coated particles from the liquid.

2. A process according to claim 1 wherein the dispersion of the pigment particles is maintained at a temperature in the range of about 80 to about 100°

C. as the solution of the acid and the solution of the soluble silicate are added thereto.

3. A process according to claim 1 wherein the soluble silicate is sodium silicate.

4. A process according to claim 1 wherein the acid is sulfuric acid.

5. A process according to claim 1 wherein the reaction mixture is maintained substantially free from aluminum.

6. A process according to claim 1 further comprising redispersing the separated silica-coated particles in an aqueous alcohol.

7. A process according to claim 1 wherein the pigment particles comprise copper chromite.

8. A process according to claim 1 wherein the silica-coated particles are treated with a silane coupling agent having a functional group capable of reacting with, and bonding to, the particles, and also having a polymerizable or polymerization initiating group, thereby causing the functional group to react with the particle surface and attach the polymerizable group thereto.

9. A process according to claim 8 wherein the silane coupling agent is a trialkoxysilane coupling agent.

10. A process according to claim 8 wherein, after treatment with the silane coupling agent, the particles are reacted with at least one monomer or oligomer under conditions effective to cause reaction between the particles and the at least one monomer or oligomer, thereby causing the formation of polymer bonded to the particle.