Ferromagnetic material powder, carrier for electrophotographic developer, process for producing them and electrophotographic developer

Abstract

A ferromagnetic material powder comprising a magnetic oxide which is a complex of a magnetite phase and a ferrite phase, wherein the ferromagnetic material powder has a spinel crystal structure and a magnetoplumbite crystal structure, and in the spinel crystal structure, the content of Fe3+ in site A is 35 to 50% and the content of Fe2+ in site B is 30 to 45%, a carrier for an electrophotographic developer, a process for producing them and an electrophotographic developer.

Description

Claims

1. A ferromagnetic material powder comprising a magnetic oxide which is a complex of a magnetite phase and a ferrite phase, the ferromagnetic material powder having a spinel crystal structure and a magnetoplumbite crystal structure, andin the spinel crystal structure, a content of Fe3+ in site A being 35 to 50% and a content of Fe2+ in site B being 30 to 45%.

2. The ferromagnetic material powder according to claim 1, wherein a content of hematite in a surface layer is 90% or less.

3. The ferromagnetic material powder according to claim 1, wherein a ratio of scattering magnetization to main magnetization is 0.8 or more.

4. The ferromagnetic material powder according to claim 1, further comprising a group 2 element in the periodic table as an element constituting the ferrite phase.

5. The ferromagnetic material powder according to claim 1, further comprising Sr and/or Ba as an element constituting the magnetoplumbite crystal structure.

6. The ferromagnetic material powder according to claim 1, wherein a raw material slurry particle size (D50) is 1.0 μm or less.

7. The ferromagnetic material powder according to claim 1, which has a strength of 75% or more.

8. The ferromagnetic material powder according to claim 1, which has a saturation magnetization of 30 to 80 A·m2/kg(emu/g).

9. The ferromagnetic material powder according to claim 1, which has an average particle size of 20 to 100 μm.

10. The ferromagnetic material powder according to claim 1, which has a resistance of 1.0×106 to 1.0×1011Ω.

11. A carrier for an electrophotographic developer, comprising the ferromagnetic material powder according to claim 1 as a core and a resin with which the surface of the ferromagnetic material powder is coated.

12. The carrier for an electrophotographic developer according to claim 11, wherein an amount of coating of the resin is 0.05 to 10% by weight.

13. A process for producing a ferromagnetic material powder, comprising pulverizing a raw material mixture containing hematite and another metal oxide to a slurry particle size (D50) of 1.0 μm or less, granulating, performing binder removing treatment, and then baking at 1100 to 1400° C. in an inert atmosphere.

14. The process for producing a ferromagnetic material powder according to claim 13, further comprising performing surface treatment in an oxidizing atmosphere after baking.

15. A process for producing a carrier for an electrophotographic developer, comprising coating the surface of the ferromagnetic material powder obtained in claim 13 with a resin.

16. An electrophotographic developer comprising the carrier according to claim 11 and a toner.