Patent ID: 8059995

Claim:
An image forming apparatus comprising: an image bearing member; and a developer bearing member bearing a developer including a toner and a carrier, the developer bearing member developing an electrostatic image formed on the image bearing member with the developer, and the developer bearing member being applied with an alternate voltage in order to form an alternate electric field between the developer bearing member and the image bearing member, wherein in a semi-logarithmic graph in which an abscissa axis represents an electric field intensity to be applied to the carrier, an ordinate axis represents a resistivity of the carrier on a logarithmic scale, letting electric field intensities Eb, Ed Eb =|( Vp 1 âˆ’VL )/ D | and Ed =|( Vp 2 âˆ’VL )/ D| (where: VL is a potential [V] of the electrostatic image for obtaining the highest density; Vp 1 , of peak potentials of the alternate voltage, is a peak potential [V] providing such a potential difference as to move the toner toward the image bearing member with respect to the VL potential; Vp 2 , of peak potentials of the alternate voltage, is a peak potential [V] providing such a potential difference as to move the toner toward the developer bearing member with respect to the VL potential; and D is the closest distance [m] between the image bearing member and the developer bearing member), and letting a gradient at Ed equal K 1 , and a gradient at Eb equal K 2 : K 1 and K 2 satisfy 0â‰§K 1 >K 2 ; and a resistivity Ïb of the carrier at the electric field intensity Eb satisfies Ïb<6.0Ã—10 7 [QÂ·m] wherein satisfied are relationships of 1.6Ã—10 6 <Eb< 3.9Ã—10 6 [V/m] and 1.6Ã—10 5 <Ed< 2.5Ã—10 6 [V/m].