Thin-film thermal head with heating resistors having self-controlled temperature

This paper describes the automatic temperature control of thermal printing elements which use metal thin films having a positive, high-temperature coefficient of resistance as heating resistors. Thermal printing elements generally require countermeasures such as input power control, because printing quality deteriorates due to heat accumulating in boards during high-speed operation. As a possible solution to this problem, automatic temperature control of the heating resistors within the heating element was studied. Further, a prototype thermal printing element has been developed which uses nickel thin film for the heating resistors. The results with the prototype clearly show that: (1) by using heating resistors with a high-temperature coefficient of resistance, automatic temperature control at the heating resistors is feasible; (2) by adding buffer resistors to the heating resistor, one can both avoid having to apply excessive voltage to the heating resistor and adjust the rate of temperature rise at the heating resistors; and (3) by fabricating the nickel thin film in a meander structure and by optimizing the operating condition for fabrication, practical heating resistors can be made which can endure thermal cycling.