Patent ID: 7912389

Claim:
An image forming apparatus, comprising: a photosensitive member; a developing device which develops an electrostatic image formed on the photosensitive member with a developer having a toner and a carrier, the developing device including a developer carrying member which carries and conveys the developer to a developing position; a transfer device which transfers a toner image formed on the photosensitive member to a transfer material; and a fixing device which fixes the toner image on the transfer material to the transfer material, wherein assuming that a toner bearing amount in a maximum density image portion of the photosensitive member is (M/S) L [mg/cm 2 ], an average charge amount of the toner in the maximum density image portion of the photosensitive member is (Q/M) L [μC/g], an absolute value of a potential difference between a potential of a DC-component of a developing bias applied to the developer carrying member and a potential of the maximum density image portion on the photosensitive member is Vc [V], a toner layer thickness of the maximum density image portion on the photosensitive member is Lt [μm], a thickness of the photosensitive member is Ld [μm], a relative permittivity of the toner layer is εt, a relative permittivity of the photosensitive member is εd, a permittivity in vacuum is ε 0 , a transmission density in a maximum density image portion on the transfer material after being fixed by the fixing device is Dtmax, a transmission density in an image portion on the transfer material when the toner bearing amount on the transfer material after being fixed by the fixing device is 0.1 mg/cm 2 is Dt 0.1 , and a transfer efficiency of the toner from the photosensitive member onto the transfer material is λ, the following formulae are satisfied: 0.22≦( M/S ) L ≦0.4, ( Q M ) L = Vc ( Lt 2 ⁢ ɛ 0 ⁢ ɛ t + Ld ɛ 0 ⁢ ɛ d ) × ( M S ) L , and assuming that α = ( Dt ⁢ ⁢ max - Dt 0.1 ) { λ × ( M S ) L - 0.1 } , and β=1/( Q/M ) L , the following formulae are satisfied: ( Dt ⁢ ⁢ max - Dt 0.1 ) { λ × ( M S ) L - 0.1 } ⁢ ( Lt 2 ⁢ ɛ 0 ⁢ ɛ t + Ld ɛ 0 ⁢ ɛ d ) × ( M S ) L 500 ≤ αβ ≤ ( Dt ⁢ ⁢ max - Dt 0.1 ) { λ × ( M S ) L - 0.1 } ⁢ ( Lt 2 ⁢ ɛ 0 ⁢ ɛ t + Ld ɛ 0 ⁢ ɛ d ) × ( M S ) L 150 ⁢ αβ = ( Dt ⁢ ⁢ max - Dt 0.1 ) { λ × ( M S ) L - 0.1 } 150 .