Patent ID: 8509668

Claim:
A fixing device comprising: a belt for heating a toner image on a recording material; a back-up member slidable on an inner surface of said belt; a pressing member for pressing said belt against said back-up member to form a nip in which the recording material is to be nip-conveyed; and a projection-recess portion, provided on a nip-forming surface of said back-up member, including a projection and a recess with respect to a recording material conveyance direction in the nip, wherein when a pressure applied when a toner temperature of the toner image reaches a softening temperature T 1 (° C.) is P 1 (kgf/cm 2 ), a pressure applied when the toner temperature reaches an incipient fluidization temperature T 2 (° C.) is P 2 (kgf/cm 2 ), the toner temperature when P(t)/η(t) wherein η(t) is a toner melt viscosity (Pa·s) and P(t) is a pressure (kgf/cm 2 ) applied with the toner melt viscosity η(t) is maximum is T 3 (° C.), and a pressure applied when the toner temperature reaches T 3 (° C.) is P 3 (kgf/cm 2 ), the following relationships 1), 2) and 3) are satisfied: 0.3 <P 1/( P 1 +P 2 +P 3), 1) 0.3 <P 2/( P 1 +P 2 +P 3), and 2) 0.2 <P 3/( P 1 +P 2 +P 3)<0.3. 3)