Thermal printing head
AssigneeThomson-CSF
InventorsChristian Val, Didier Pribat
Life of this patent
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Abstract
An electrical heating resistor of the type deposited on a substrate plate constituting the basis element of a thermal printing head. In order to concentrate the heat given off in the free surface of said heating resistor towards the paper to print, the invention provides for the deposition on the substrate of at least one layer having a relatively constant resistivity and then at least one surface layer with a non-linear resistivity and a negative temperature coefficient. Starting from a high value when cold, the resistance of the surface layer drops abruptly as soon as it reaches the triggering temperature, thus switching the heat resistor by command of a control circuit.
Claims6
A thermal printing head comprising at least one strip of linear heating resistors, wherein each resistor is deposited on an insulating glass or ceramic substrate, whose thermal capacity is well above that of the heating resistor, and wherein it comprises at least a first layer of a material having a relatively constant resistivity as a function of the temperature and which is deposited in direct contact with the substrate and at least a second surface layer of a material whose resistivity varies in non-linear manner with the temperature and having a negative temperature coefficient, said second layer being deposited on the first layer.
Dependencies are inferred from the claim text.