Patent ID: 8391766

Claim:
A fixing device that fixes a toner image in place on a recording medium, the fixing device comprising: a cylindrical first member extending along a first longitudinal axis, a thickness of an external circumferential surface of the first member varying along the first longitudinal axis to define at least one first convex portion curving outward and at least one first concave portion curving inward with respect to the first longitudinal axis, a thickness of the first convex portion being larger than a thickness of the first concave portion; a second member extending along a second longitudinal axis parallel to the first longitudinal axis, a thickness of an external circumferential surface of the second member varying along the second longitudinal axis to define at least one second convex portion curving outward and at least one second concave portion curving inward with respect to the second longitudinal axis, at least one of the first and second members being pressed against the other of the first and second members, with the first convex portion engaging the second concave portion and the first concave portion engaging the second convex portion, to define a fixing nip therebetween through which the recording medium is passed to fix the toner image under heat and pressure; and a heating source disposed in the first member to heat the first member, wherein, when the heating source heats the first member, a temperature of an inner circumference side of the first convex portion is higher than a temperature of an inner circumference side of the first concave portion, wherein an inner surface of the first member is coated in a paint so that a heat absorptivity of an inner surface of the first convex portion is higher than a heat absorptivity in an inner surface of the first concave portion.