Electrographic methods using hard magnetic carrier particles

• US 6,589,703 B2
• Filed: 05/11/2001
• Issued: 07/08/2003
• Est. Priority Date: 05/17/2000
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Heidelberger Druckmaschinen Ag
• Inventors: Stelter, Eric C., Fields, Robert D., Jadwin, Thomas A.
• Primary Examiner(s): Chapman, Mark A.
• Application Number:
  US09/853,412
• Publication Number:
  US 20010055723A1
• Time in Patent Office: 788 Days
• Field of Search: 430/122, 430/111.3, 430/111.31
• US Class Current: 430/122.3
• CPC Class Codes: G03G 15/0928 relating to the shell, e.g. structure, composition
• CPC Class Codes: G03G 9/09708 Inorganic compounds
• CPC Class Codes: G03G 9/09716 treated with organic compounds
• CPC Class Codes: G03G 9/09725 Silicon-oxides; Silicates
• CPC Class Codes: G03G 9/09733 Organic compounds G03G9/08782 takes precedence
• CPC Class Codes: G03G 9/1085 with non-ferrous metal oxide, e.g. MgO-Fe2O3

Abstract

Disclosed are methods and apparatus for electrographic development which utilize a rotating magnetic core, a toner shell disposed around the rotating magnetic core, and developer compositions disposed on the toner shell which include a hard magnetic material, such as a strontium ferrite. The shell in embodiments has an outer surface with a surface roughness Ra of less than 32 microinches. The methods and apparatus do not require special manufacturing steps to place surface roughness or irregularities on the shell, and, thus, can provide the same or better image quality with relatively less complex manufacturing steps and at reduced cost.

Claims

1. A method for development of an electrostatic image comprising contacting the image with at least one magnetic brush comprising:

(a) a rotating magnetic core of a pre-selected magnetic field strength;

(b) an outer nonmagnetic shell disposed about the rotating magnetic core; and

(c) an electrographic developer composition disposed on an outer surface of the shell and in contact with the image, the developer composition comprising a mixture of charged toner particles and oppositely charged carrier particles comprised of a hard magnetic material, the toner particles having dispersed on the outer surfaces thereof at least one surface-treatment agent selected from the group consisting of;

beads of a polymer selected from acrylic polymers, styrenic polymers, silicone-based polymers, and fluoropolymers;

hydrophobic silica that has been surface treated with silicone oil or hexamethyldisilazane; and

mixtures thereof.

2. The method of claim 1 wherein the surface treatment agent comprises beads of a polymer selected from acrylic polymers, styrenic polymers, silicone-based polymers, and fluoropolymers, further wherein the beads have a volume average diameter of less than about 0.1 μ

m.

3. The method of claim 1 wherein the silica has a BET surface area of at least about 50 m²/g prior to the hydrophobizing surface treatment of the silica.

4. The method of claim 1 wherein the silica has a BET surface area of from about 100 to about 410 m²/g prior to the hydrophobizing surface treatment of the silica.

5. The method of claim 1 wherein the surface treatment agent is employed in an amount of from about 0.05 to about 5.0 wt % based on total weight of the toner.

6. The method of claim 1 wherein the surface treatment agent is employed in an amount of from about 0.1 to about 2 wt % based on total weight of the toner.

7. The method of claim 1 wherein the surface treatment agent is employed in an amount of from about 0.15 to about 1.5 wt % based on total weight of the toner.

8. The method of claim 1 wherein the toner particles have an average particle size of from about 4 to about 12 μ

m.

9. The method of claim 1 wherein the hard magnetic material exhibits a coercivity of at least about 300 gauss when magnetically saturated and has an induced magnetic moment of at least about 20 EMU/gm when in an externally applied field of 1,000 gauss.

10. The method of claim 1 wherein the hard magnetic material is a hard magnetic ferrite.

11. The method of claim 10 wherein the hard magnetic ferrite is selected from strontium ferrite or barium ferrite.

12. The method of claim 10 wherein the hard magnetic material is strontium ferrite.

13. The method of claim 1 wherein the toner comprises a polymer resin selected from polyesters or polystyrene-acrylate copolymers.

14. The method of claim 1 wherein the outer surface of the shell has a surface roughness Ra of less than about 32 microinches.

15. The method of claim 1 wherein the outer surface of the shell has a surface roughness Ra of less than about 12 microinches.

16. The method of claim 1 wherein the method operates at a process speed of about 17.5 inches/sec or greater.

17. A method for development of an electrostatic image comprising contacting the image with at least one magnetic brush comprising:

(a) a rotating magnetic core of a pre-selected magnetic field strength;

(b) an outer nonmagnetic shell having a smooth outer surface thereon with a surface roughness of roughness Ra of less than about 32 microinches; and

(c) an electrographic developer composition disposed on the smooth outer surface of the shell and in contact with the image, the developer composition comprising a mixture of charged toner particles and oppositely charged carrier particles comprised of a hard magnetic material, the toner particles having dispersed on the outer surfaces thereof at least one surface-treatment agent.

18. The method of claim 17 wherein the surface treatment agent is selected from silica, titania, alumina, and zirconia.

19. The method of claim 17 wherein the surface treatment agent is silica.

20. The method of claim 17 wherein the surface treatment agent are beads of a polymer selected from acrylic polymers, styrenic polymers, silicone-based polymers, fluoropolymers and mixtures thereof.

21. The method of claim 20 wherein the beads have a volume average diameter of less than about 0.1 μ

m.

22. The method of claim 19 wherein the silica is a hydrophobic silica that has been surface treated with dichlorodimethylsilane, silicone oil, or hexamethyldisilazane.

23. The method of claim 22 wherein the silica has a BET surface area of at least about 50 m²/g prior to the hydrophobizing surface treatment of the silica.

24. The method of claim 22 wherein the silica has a BET surface area of from about 100 to about 410 m²/g prior to the hydrophobizing surface treatment of the silica.

25. The method of claim 17 wherein the surface treatment agent is employed in an amount of from about 0.05 to about 5.0 wt % based on total weight of the toner.

26. The method of claim 17 wherein the surface treatment agent is employed in an amount of from about 0.1 to about 2 wt % based on total weight of the toner.

27. The method of claim 17 wherein the surface treatment agent is employed in an amount of from about 0.15 to about 1.5 wt % based on total weight of the toner.

28. The method of claim 17 wherein the toner particles have an average particle size of from about 4 to about 12 μ

m.

29. The method of claim 17 wherein the hard magnetic material exhibits a coercivity of at least about 300 gauss when magnetically saturated and has an induced magnetic moment of at least about 20 EMU/gm when in an externally applied field of 1,000 gauss.

30. The method of claim 17 wherein the hard magnetic material is a hard magnetic ferrite.

31. The method of claim 30 wherein the hard magnetic ferrite is selected from strontium ferrite or barium ferrite.

32. The method of claim 30 wherein the hard magnetic material is strontium ferrite.

33. The method of claim 17 wherein the toner comprises a polymer resin selected from polyesters or polystyrene-acrylate copolymers.

34. The method of claim 17 wherein the outer surface of the shell has a surface roughness Ra of less than about 12 microinches.

35. The method of claim 17 wherein the method operates at a process speed of about 17.5 inches/sec or greater.