Patent ID: 7010257

Claim:
A fixing unit comprising: a first fixing member that faces a surface of a recording medium on which an unfixed toner layer is held; a second fixing member that is in a pressurized contact with the first fixing member so as to form a fixing nip theirbetween; and a heating unit that heats the unfixed toner layer from a side of the first fixing member so as to fix the unfixed toner layer on the recording medium, wherein if a difference between a lower limit temperature T MIN for fixing of a surface of the first fixing member that satisfies a fixity and a minimum temperature T OFF of the surface of the first fixing member at which a hot offset occurs at an exit of the fixing nip when a fixing time, in seconds, that is obtained by dividing a width, in meters, of the fixing nip by a velocity, in m/s, of carrying the recording medium through the fixing nip is set to 1 second is let to be T 0 , following conditions are satisfied: (1) 2.4×10 3 ×d/(TC×t)<T 0 , where d is a thickness of the unfixed toner layer in meters, TC is a thermal conductivity of toner in W/mK, and t is the fixing time in seconds, (2) a temperature T top of a topmost layer of the toner layer is not greater than the minimum temperature T OFF at which the hot offset of the surface of the first fixing member occurs when the fixing time is set to 1 seconds, and (3) a temperature T bot of a bottommost layer of the toner layer that is in contact with the recording medium is not less than the lower limit temperature T MIN for fixing of the surface of the first fixing member when the fixing time is set to 1 second.