Patent ID: 8175508

Claim:
A planar heat generating element for use in a fixing device for fixing a toner image borne on a recording medium onto the recording medium under application of heat and pressure, the planar heat generating element comprising: an insulating layer; a resistance heat generator formed on one surface in a thickness direction of the insulating layer, for generating heat upon a passage of electric current therethrough, the resistance heat generator constituting a plane of certain configuration as a whole and forming a heat generating pattern, the resistance heat generator comprising: a plurality of linear portions formed on the one surface of the insulating layer so as to extend transversely with respect to a longitudinal of the insulating layer, the plurality of linear portions being arranged side by side substantially in parallel with one another; and a low-volume resistivity portion formed on the one surface of the insulating layer so as to extend in the longitudinal direction of the insulating layer, for connecting adjacent linear portions at their extending direction-wise ends to form a single line composed of the adjacent linear portions and the low-volume resistivity portion, the low-volume resistivity portion being made of a material which is lower in volume resistivity than a material for forming the linear portion, wherein the heat generating pattern is formed so as to be divided into plural pieces in the longitudinal direction of the insulating layer, and wherein, in two pieces among the plural pieces, the two pieces being each located at longitudinal end portions of the planar heat generating element, intervals among the plurality of linear portions adjacent to one another are set so as to become smaller from the center of the planar heat generating element toward each end thereof.