Thermal head, method of manufacturing the same, and thermal stencil making apparatus using the same

A thermal head comprising a heat radiating plate and an electrical insulating substrate which is provided with a plurality of resistance heater elements arranged in a direction over a predetermined length and a plurality of electrodes for energizing the resistance heater and is integrated with the heat radiating plate, wherein the improvement comprises that the substrate is smaller than the heat radiating plate in coefficient of thermal expansion and is fixed to the heat radiating plate at a temperature higher than the normal working temperature range of the thermal head so that the thermal head is convex toward the resistance heater, in a cross-section taken along a line parallel to the direction in which the resistance heater elements are arranged, in the normal working temperature range of the thermal head due to the difference in coefficient of thermal expansion between the heat radiating plate and the substrate.

A thermal stencil making apparatus comprising a thermal head and a platen roller against which the thermal head is pressed with a stencil material intervening therebetween, wherein the improvement comprises that the thermal head comprises a heat radiating plate and an electrical insulating substrate which is provided with a plurality of resistance heater elements arranged in a direction over a predetermined length and a plurality of electrodes for energizing the resistance heater and is integrated with the heat radiating plate, and the substrate is smaller than the heat radiating plate in coefficient of thermal expansion and is fixed to the heat radiating plate at a temperature higher than the normal working temperature range of the thermal head so that the thermal head is convex toward the resistance heater, in a cross-section taken along a line parallel to the direction in which the resistance heater elements are arranged, in the normal working temperature range of the thermal head due to the difference in coefficient of thermal expansion between the heat radiating plate and the substrate.

A method of manufacturing a thermal head comprising a heat radiating plate and an electrical insulating substrate which is provided with a plurality of resistance heater elements arranged in a direction over a predetermined length and a plurality of electrodes for energizing the resistance heater and is integrated with the heat radiating plate, the method comprising the steps of heating a heat radiating plate of metal and an electrical insulating substrate which is smaller than the heat radiating plate in coefficient of thermal expansion to a temperature higher than the normal working temperature range of the thermal head, and fixing the heated substrate to the heated heat radiating plate and cooling them so that the thermal head is convex toward the resistance heater, in a cross-section taken along a line parallel to the direction in which the resistance heater elements are arranged, in the normal working temperature range of the thermal head due to the difference in coefficient of thermal expansion between the heat radiating plate and the substrate.