Patent attributes
A fixing device (23) of the present invention includes a fixing roller (131) contacting a toner image surface, and a pressure roller (132) contacting a surface opposite to the toner image surface. In the fixing device (23), a printing sheet (P) on which unfixed toner image is formed passes through a fixing nip portion (Y) where the fixing roller (131) and the pressure roller (132) are in contact with each other, so that the above-described toner image is fixed on the printing sheet (P). The fixing device (23) further includes a control circuit (150) which controls heater lamps (134 to 136) so that a surface temperature of the pressure roller (132) is in a temperature range defined by a cold offset occurring boundary temperature (Thc) of the fixing roller (131) and/or a hot offset occurring boundary temperature (Thh) of the fixing roller (131). With this, it is possible to suppress or prevent a transfer of toner to a pair of rollers (a transfer from the back of the printing sheet to the pressure roller, a transfer from the pressure roller to the fixing roller).
