Developing device and electrophotographic apparatus using the same
View Patent ↗An electrophotographic apparatus includes: a photoconductor; and two developing rollers facing the photoconductor. A developer fed out from between the two developing rollers is supplied to the photoconductor by the two developing rollers to form a toner image on the photoconductor. The developer includes a carrier having a volume-average particle size smaller than 70 μm and a volume resistivity not lower than 10 6 Ω·cm. A volume ratio of the carrier in a facing portion between the photoconductor and the developing rollers is not lower than 30% and not higher than 46%.
1. An electrophotographic apparatus comprising:
a photoconductor; and
two developing rollers facing the photoconductor,
wherein a developer fed out from between the two developing rollers is supplied to the photoconductor by the two developing rollers to form a toner image on the photoconductor,
wherein the developer includes a carrier having a volume-average particle size less than 70 μm and a volume resistivity of at least 10 6 Ω·cm,
wherein a volume ratio of the carrier in a facing portion between the photoconductor and the developing rollers is in a range of 30% to 46%,
wherein the carrier has a volume resistivity of at least 10 12 Ωcm when an intensity of an applied electric field is 1000 V/cm and a volume resistivity of equal to or less than 10 10 Ωcm when the intensity of the applied electric field is 10000 V/cm.
2. The electrophotographic apparatus according to claim 1 , wherein the carrier has a surface coated with a resin.
3. The electrophotographic apparatus according to claim 1 , wherein the carrier has a surface coated with a resin having an electrically conductive material.
4. The electrophotographic apparatus according to claim 1 , wherein the carrier has a core material comprising iron powder, said iron powder comprising iron oxide as a main component.
5. The electrophotographic apparatus according to claim 1 , wherein the carrier has a core material comprising a ferrite carrier, said ferrite carrier including a metal oxide other than iron oxide as a subsidiary component.
6. The electrophotographic apparatus according to claim 5 , wherein the ferrite carrier comprises a magnesium ferrite carrier, said magnesium ferrite carrier comprising magnesium oxide as a subsidiary component.
7. The electrophotographic apparatus according to claim 1 , wherein the carrier has a core material comprising a binder carrier, said binder carrier comprising one of:
a kneaded iron powder-resin product; and
a kneaded ferrite fine powder-resin product.
8. The electrophotographic apparatus according to claim 1 , wherein said two developing rolls rotate in different directions.
9. The electrophotographic apparatus according to claim 1 , wherein said two developing rolls comprise:
a first developing roll; and
a second developing roll formed underneath said first developing roll,
wherein said first developing roll rotates such that a moving direction of a surface of said first developing roll is reverse to a moving direction of a surface of said photoconductor; and
wherein said second developing roll rotates such that a moving direction of a surface of said second developing roll is that of the moving direction of said surface of said photoconductor.
10. A developer for an electrophotographic apparatus, comprising:
a toner; and
a carrier, said carrier having a volume-average particle size smaller than 70 μm, a volume resistivity of at least 10 6 m, a volume resistivity of at least 10 12 Ωm when an intensity of an applied electric field is 1000 V/cm, and a volume resistivity of equal to or less than 10 10 Ωm when the intensity of the applied electric field is 10000 V/cm.
11. The developer according to claim 10 , wherein said electrophotographic apparatus comprises:
two developing rolls for distributing said two-component developer;
a conveyance roll for carrying said two-component developer to said two developing rolls;
a limiting member for carrying said two-component developer from said two developing rolls to a photoconductor; and
a blade for removing an excess amount of said two-component developer, said excess amount returned to said developing device.
12. The developer according to claim 11 , wherein said two developing rolls rotate in different directions.
13. The developer according to claim 11 , wherein said two developing rolls comprise:
a first developing roll; and
a second developing roll formed underneath said first developing roll,
wherein said first developing roll rotates such that a moving direction of a surface of said first developing roll is reverse to a moving direction of a surface of said photoconductor; and
wherein said second developing roll rotates such that a moving direction of a surface of said second developing roll is that of the moving direction of said surface of said photoconductor.
14. The developer according to claim 10 , wherein the carrier has a surface coated with a resin.
15. The developer according to claim 10 , wherein the carrier has a surface coated with a resin comprising an electrically conductive material.
16. The developer device according to claim 10 , wherein the carrier comprises a core material comprising iron powder, said iron powder comprising iron oxide as a main component.
17. The developer according to claim 10 , wherein the carrier has a core material comprising a ferrite carrier, said ferrite carrier including a metal oxide other than iron oxide as a subsidiary component.
18. The developer according to claim 17 , wherein the ferrite carrier comprises a magnesium ferrite carrier, said magnesium ferrite carrier comprising magnesium oxide as a subsidiary component.
19. The developer according to claim 10 , wherein the carrier comprises a core material comprising a binder carrier, said binder carrier comprising one of:
a kneaded iron powder-resin product; and
a kneaded ferrite fine powder-resin product.