A maximum curvature in a rotational direction of a fixing belt and the number of times of bendings when a temperature of the fixing belt is equal to or lower than a glass transition temperature of the fixing belt surface material are specified, and the fixing belt controlled to operate within the specified range.

An image fixing device for fixing an image on a sheet includes a rotatable fixing film; a heater provided on an inner surface of the fixing belt; a rotatable pressing member provided in contact with an outer peripheral surface of the film to press against the heater through the film, thus forming a nip configured to nip and feed the sheet; a holding member including a guide portion configured to guide the rotation of the fixed in the field and to hold the heater; and a metal sheet which covers the heater and an area of guide portion slidable relative to the film and which is slidable on an inner surface of the film. The metal sheet has a thermal conductivity 10 W/(m.Math. C.) and has a thickness more than 0 m and not more than 50 m.

A fixing device includes: a belt; a heating element that heats the belt; and a pressure member that faces the belt and forms a nip portion between the pressure member and the belt. A dielectric relaxation rate of the belt 10 seconds after applying a corona discharge at 7000V to the belt is greater than or equal to 9.5% and less than or equal to 28.9%.

A fixing device includes: a belt; a heating element that heats the belt; and a pressure member that faces the belt and forms a nip portion between the pressure member and the belt. A dielectric relaxation rate of the belt 10 seconds after applying a corona discharge at 7000 V to the belt is greater than or equal to 9.5% and less than or equal to 28.9%.

A fixing apparatus will be described for fixing a toner image on a recording medium. The apparatus includes a heater that is in contact with an inner surface of a film, a restricting member that restricts movement of the film in a longitudinal direction of the film, a connector that is connected electrically to the heater for supplying electric power to the heater, and a lock member that maintains a position of the restricting member and a position of the connector relative to each other.

An image forming apparatus includes an image forming portion that forms a toner image on a recording material, and a first rotatable member and a second rotatable member, which form a nip therebetween in which the toner image, formed on the recording material by the image forming portion, is heated. A belt unit includes an endless belt that externally heats the first rotatable member, and a supporting mechanism rotatably supporting the endless belt. A moving mechanism moves the belt unit so as to be movable between a contact position and a spaced position. In addition, a controller executes a process in which one of the belt unit with a new endless belt and a new belt unit with a new endless belt is moved to the contact position, and then, the new endless belt is rotated for a predetermined time by the first rotatable member.

An image forming apparatus includes a resistive heat generator, a temperature detector, and a power controller that detects a temperature-resistance property of the resistive heat generator before the resistive heat generator is used when the resistive heat generator is removably installed. The power controller obtains power supplied to the resistive heat generator and a change in a temperature of the resistive heat generator, that is detected by the temperature detector, while the power controller supplies the power at a predetermined power duty cycle for adjustment to the resistive heat generator. The power controller calculates the temperature-resistance property of the resistive heat generator based on the power and the change in the temperature that are obtained. The power controller adjusts a power duty cycle at which the power is supplied to the resistive heat generator in use of the resistive heat generator, based on the temperature-resistance property.

A fixing belt is heated by a heater in contact with an inner circumferential face through a lubricant while rotating about an axis. The fixing belt includes: a belt body formed in a tubular shape; a plurality of oil repellent portions formed on an inner circumferential face of the belt body, each having a surface free energy lower than that of the lubricant to repel the lubricant; and a plurality of oil nonrepellent portions formed on the inner circumferential face of the belt body, each having a surface free energy higher than that of the lubricant to hold the lubricant. The oil repellent portions and the oil nonrepellent portions extend in a circumferential direction of the belt body and are alternately arranged in an axial direction of the belt body.

A fuser device for fusing a developer image on a medium by applying heat includes an endless fuser belt, a belt supporting part that has a contact face shaped in an arc centering on a first central axis and contacts with the inner circumferential face of the fuser belt on the contact face, a driven ring that is disposed on at least one side of the fuser belt in the width direction of the fuser belt, and a ring supporting part that has a contact face shaped in an arc centering on a second central axis and contacts with an inner circumferential face of the driven ring on the contact face, wherein the first central axis is shifted from the second central axis.

A fixing belt is heated by a heater in contact with an inner circumferential face through a lubricant while rotating about an axis. The fixing belt includes: a belt body formed in a tubular shape; a plurality of oil repellent portions formed on an inner circumferential face of the belt body, each having a surface free energy lower than that of the lubricant to repel the lubricant; and a plurality of oil nonrepellent portions formed on the inner circumferential face of the belt body, each having a surface free energy higher than that of the lubricant to hold the lubricant. The oil repellent portions and the oil nonrepellent portions extend in a circumferential direction of the belt body and are alternately arranged in an axial direction of the belt body.