(57) A thermal head printer for printing but not perforating a substantially light-insensitive
thermographic material, the thermal printer comprising: a transport system having
a transport direction, n thermal heads, where n is an integer, each of the thermal
heads comprising an array of substantially rectangular energizable heating elements,
the heating elements having a length Ln in the transport direction and a pitch Pn between adjacent heating elements, and a means for supplying electrical energy to
each of the substantially rectangular energizable heating elements in at least one
of the thermal heads, the transport system being capable of transporting the light-insensitive
thermographic material in contact or proximity with at least one of the thermal heads,
characterized in that at least one of the thermal heads comprises heating elements
for which Ln/Pn is between 0.25 and 0.88; a first process for printing a substantially light-insensitive
thermographic material with the above-described thermal head printer; a second process
for printing a substantially light-insensitive thermographic material at different
printing speeds with a thermal head comprising heating elements without significant
variation in image tone, characterized in that the length of the heating elements
in the transport direction of the substantially light-insensitive thermographic material
decreases with decreasing printing speed; and a third process for printing a substantially
light-insensitive thermographic material at different printing speeds with a different
thermal head at each printing speed without significant variation in image tone, characterized
in that each of said different thermal heads comprises heating elements with a different
length in the transport direction of the substantially light-insensitive thermographic
material and the length of the heating elements in the transport direction of the
substantially light-insensitive thermographic material decreases with decreasing printing
speed.
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