Sheet heater and image fixing device including the sheet heater

A sheet heater comprising:

• a sheet article composed of a conductive resin composition containing a conductive material and a resin;
• and
• a pair of metal plate electrodes, one of the electrodes being bonded to one end of the sheet article, the other electrode being bonded to the other end of the sheet article, wherein
• when elements of the sheet article are detected at a portion 1 μm depth from a surface of the metal plate electrode, a peak area ratio of silicon (Si) to metal ion (M) is 1/100 to 1, the metal ion M being most abundant of all metal ions detected at the portion, the peaks being obtained by measuring an X ray generated at the portion by applying an X ray to the portion with the scanning electron microscope-energy dispersive X-ray spectrometer.