OPTIMIZATION OF THE THERMAL PERFORMANCE OF A PRINTHEAD STRUCTURE FOR PULSE-COUNT-MODULATED DYE DIFFUSION THERMAL PRINTING

The heat produced in the printhead of a dye diffusion thermal printer is governed by numerous factors, including the power generated in the heating elements, the current pulsing scheme used to modulate the imag e pixel optical density, and the line printing time. In addition, the heat generated is strongly influenced by the structure of the printhea d, in particular by the thickness and thermal conductivity of the ther mal insulation layer on which the resistors lie. The principal tempera ture constraints in the printing system are the glass transition tempe rature of the receiving layer, which is the minimum, and the distortio n temperature of the receiving layer, which is the maximum. A simple a lgorithm, derived from a numerical transient beat conduction analysis of the structure, is proposed to optimize the thermal performance of a thermal printhead, which uses a pulse-count-modulated head driver met hod with its characteristic line printing time, duty cycle, and number of tone scale levels. Whereas the lowest insulation layer thermal con ductivity is desirable, with that minimum value there is a correspondi ng optimum thickness that compromises between the required power and t he temperature rise time.