A planar heater includes a base, a resister pattern, a conductor pattern, a power supply electrode, and a base pattern. The base includes a surface portion made of an insulative material. The resistor pattern is on the base. The conductor pattern is on the base and electrically coupled to the resistor pattern. The power supply electrode is electrically coupled to the conductor pattern. The base pattern is on the base and made of a material different from a material of the surface portion of the base to print visible identification information.

A fixing device includes a fixing belt, a pressure applying member, and a heater holding member. The fixing belt fixes toner to a sheet. The pressure applying member forms a nip portion together with an outer peripheral surface of the fixing belt and causes the fixing belt to peripherally rotate while applying pressure to the fixing belt at the nip portion. The heater holding member holds a heater that applies heat to the fixing belt. The heater holding member includes: a side portion that extends from the nip portion along an inner peripheral surface of the fixing belt and guides the fixing belt; and a plurality of inclined ribs that are disposed on the side portion to face the inner peripheral surface and formed such that an interval between them is gradually narrowed as they proceed in a direction in which the fixing belt peripherally rotates.

A fixing device, including: a cylindrical belt; a heater including a base plate and a heating element provided on the base plate; a holder supporting the heater; and a heat-conductive member disposed between the heater and the holder and having a higher heat conductivity than the base plate, wherein the heat-conductive member includes: a contact portion opposed to a region of the base plate between a one-side end and an other-side end of the heating element in the first direction; a first non-contact portion opposed to a region of the base plate in which the one-side end is located, the first side portion being not in contact with the heater, and a second non-contact portion opposed to a region of the base plate in which the other-side end is located, the second side portion being not in contact with the contact portion.

A fusing device includes: an endless rotatable fusing belt; a nip forming member that is disposed on an inner circumferential surface of the fusing belt; a pressure roller that is in pressure contact with the nip forming member from an outer side of the fusing belt and forms a fusing nip area between the pressure roller and the fusing belt; and a heat source that is disposed inside the fusing belt and heats the fusing belt. The fusing device further includes a heat-conductive member that is disposed on a lateral side of an outer circumference of the fusing belt. The heat-conductive member extends over a width area in a rotation axis direction of the fusing belt.

A fixing device includes a heater including a substrate and a resistance heating element disposed on the substrate, an endless belt, a first temperature sensor disposed at a position opposed to the heater and configured to detect a temperature at a center part of the heater in a longitudinal direction of the heater; and a second temperature sensor disposed at a position opposed to the heater and configured to detect a temperature at an end part of the heater in the longitudinal direction of the heater. The second temperature sensor is disposed at a position located on an outer side of the resistance heating element in the longitudinal direction of the heater.

A fixing device includes a heater including a substrate and a resistance heating element, an endless belt, a holder, a first heat conductive member and a second heat conductive member arranged in a longitudinal direction of the heater such that a first end of the first heat conductive member and a second of the second heat conductive member in the longitudinal direction of the heater are adjacent to each other, a temperature sensor configured to detect a temperature at an end part of the heater. The temperature sensor is in contact with the first heat conductive member. A position located between first end of the first heat conductive member and the second end of the second heat conductive member is closer to the temperature sensor than a central position of the resistance heating element in the longitudinal direction of the heater.

An image heating device comprising: a first rotating member, a heater, a heater holder, and a second rotating member, wherein the heater holder has a flat surface portion provided downstream of the heater in a conveying direction of a recording material, the flat surface portion being in contact with the inner peripheral surface of the first rotating member, wherein the flat surface portion has a first region and a second region in a longitudinal direction, wherein the first region includes a region corresponding to a region of a nip portion through which a central portion of the recording material passes, and the second region is a region on an end portion side from the first region in the longitudinal direction, and wherein in the conveying direction, the downstream end portion of the second region is located upstream of the downstream end portion of the first region.

A heater includes: a substrate; a heating element, provided on a first surface of the substrate and extending in a longitudinal direction of the substrate; a protection part, provided on the first surface, extending in the longitudinal direction of the substrate, and covering the heating element; and at least one relaxation part, provided on a second surface of the substrate facing the first surface. A coefficient of thermal expansion of the protection part and a coefficient of thermal expansion of the at least one relaxation part are different from a coefficient of thermal expansion of the substrate. A material of the at least one relaxation part is the same as a material of the protection part, or a main component of the material of the at least one relaxation part is the same as a main component of the material of the protection part.

A fixing device includes a substrate, a first heat generator, a second heat generator with a length in a longitudinal direction of the substrate equal to a length of the first heat generator; and a third heat generator with a length shorter than the lengths of the first and second heat generators, a soaking member with a positioning portion in the longitudinal direction. In a short side direction of the substrate, the first heat generator is arranged at one end side, the second heat generator is arranged at the other end side, and the third heat generator is arranged between the first and second heat generators. The soaking member is arranged between the heater and a holder in a thickness direction. As seen in the short side direction, the positioning portion is positioned outside of an area corresponding to the third heat generator and inside of an area corresponding to the first heat generator.

A fixing device includes a cylinder, a heater, a contact body, and a soaking member. The heater has a first surface and an opposing second surface. The heater includes a heating element extending along a longitudinal direction of the heater. The first surface engages with an inner surface of the cylinder. The contact body is configured to engage with the inner surface of the cylinder. The contact body is configured to be heated at a first position along the longitudinal direction at a first temperature increase rate and at a second position along the longitudinal direction at a second temperature increase rate that is lower than the first temperature increase rate. The soaking member is positioned to engage with the opposing second surface of the heater. The soaking member has a second thermal capacity lower than a first thermal capacity at the respective second and first positions.