There are adopted an electrophotographic resin-coated ferrite carrier having a carrier core coated with a resin, wherein a product of an apparent density ρ (g/cm3), average particle size d (μm) and BET specific surface area S (m2/g) of the carrier core satisfies the following condition, a method for producing the same, and an electrophotographic developer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates an electric resistance measuring apparatus used for measuring the electric resistance of a carrier core (ferrite particles).
Claims
1. An electrophotographic resin-coated ferrite carrier having a carrier core coated with a resin, wherein a product of an apparent density ρ (g/cm3), average particle size d (μm) and BET specific surface area S (m2/g) of the carrier core satisfies the following condition.
4.5 ≦ρ×d ×S≦8.5 (20≦d≦45)
2. The electrophotographic resin-coated ferrite carrier according to claim 1, wherein at 1 KOe, a bulk magnetization A of the carrier core is 50 to 70 Am2/kg; a difference (A−B) between the bulk magnetization A and a debris magnetization B thereof is 10 Am2/kg or less; and a percent inclusion of a carrier core having a magnetization at least 10 Am2/kg lower than the bulk magnetization A is 50 ppm or less.
3. The electrophotographic resin-coated ferrite carrier according to claim 1, wherein the carrier core has a shape factor SF-1 of 100 to 120.
4. The electrophotographic resin-coated ferrite carrier according to claim 1, wherein the carrier core has a particle size distribution CV value of 23 or less.
5. The electrophotographic resin-coated ferrite carrier according to claim 1, wherein the carrier core has a resistance of 105 to 109 Ω at 1000 V.
6. The electrophotographic resin-coated ferrite carrier according to claim 1, wherein the carrier core is coated with 0.1 to 10% by weight of the resin.
7. A method for producing an electrophotographic resin-coated ferrite carrier, comprising the steps of:
grinding, mixing and pelletizing ferrite raw materials;preliminarily baking the pellets at 900 to 1200° C.;grinding the preliminarily fired pellets;producing a slurry from the resulting particles;granulating the obtained slurry;baking the granules at 1100 to 1450° C. for 1 to 24 hours under an oxygen concentration of 0 to 21 vol. % to obtain a carrier core having an average particle size of 20 to 45 μm; andcoating the obtained carrier core with a resin,wherein slurry particle sizes, D50 and D90, of the slurry are 3.0 μm or less and 4.0 μm or less, respectively.
8. The method for producing the electrophotographic resin-coated ferrite carrier according to claim 7, wherein the slurry particle sizes, D50 and D90, of the slurry are 2.0 μm or less and 3.0 μm or less, respectively.
9. The method for producing the electrophotographic resin-coated ferrite carrier according to claim 7, wherein a difference in temperature between the baking and the preliminary baking is 280° C. or less.
10. An electrophotographic developer comprising the resin-coated ferrite carrier according to claim 1 and a toner.
Patent Application
20070231732
