Ceramic heater for toner-fixing units and method for manufacturing the heater

A method for manufacturing a ceramic heater for a toner-fixing unit which unit:

• (a) comprises:
• (a1) a heating cylinder provided with a ceramic heater along the longitudinal direction of the outer surface of the cylinder;
• (a2) a continuous heat-resistant film revolving along the periphery of the heating cylinder;
• and
• (a3) a pressure roller that forms a nip portion together with the heat-resistant film at the outer region of the roller opposite to the ceramic heater on the heating cylinder and that rotates to revolve the heat-resistant film at the same speed as the peripheral speed of the pressure roller;
• (b) feeds a copying sheet to the nip portion by the revolution of the heat-resistant film and the pressure roller;
• and
• (c) fixes a toner image on the copying sheet by the pressure of the pressure roller and the heat from the ceramic heater on the heating cylinder;
• the method comprising the steps of:
• (d) extruding a material for a ceramic base material to obtain a formed body in a manner such that at least one part of the ceramic-base-material's face that contacts the heat-resistant film is curved when viewed from a direction perpendicular to the feeding direction of the copying sheet;
• (e) sintering the formed body;
• and
• (f) providing a silver or silver-alloy heating element and silver or silver-alloy current-feeding electrodes on the ceramic base material at the face where the ceramic base material contacts the heat-resistant film or at the back face.