Printronix T4204 - Manual (Page 15)

15
Thermal Printer Technology
Quiet and fast, with excellent print quality, the T4204 multifunction label
printer uses an inline thermal printhead. The operation of a thermal printer is
different from that of a line-matrix or laser printer. The thermal printer uses a
printhead with heating elements and special paper or ribbon.
The Printing Process
The thermal printhead allows two modes of operation:
• Direct Thermal
During direct thermal printing, the thermal printhead selectively heats
small, rectangular thermal dots. When these contact the coated thermal
paper, the dyes and developers in the coating react to the heat and
develop an image. This mode of printing is generally used for short-term
labeling applications.
• Thermal Transfer
During thermal transfer printing, the heated thermal dots contact a
thermal ribbon. The heat reacts with the ribbon and bonds the image to
the paper. This method is used especially for abrasive, long-storage
applications and for specialized applications, such as in extreme
environmental conditions or where tamper-proofing is required.
Dynamic Print Control
Print quality largely depends on how the thermal paper or the thermal ribbon
and thermal transfer paper responds to the heat of the thermal printhead.
During printing, the thermal printhead must reach a set temperature in the
shortest possible time. Then it must cool down to the original temperature in
the shortest possible time after printing. Thus print quality is dependent on the
precise control of the energy supplied to the thermal dots.
The thermal printer has a unique feature that provides excellent print quality
by preventing unevenness of print density. Unevenness is usually caused by
the stored heat from previous dots. The Dynamic Print Control is a history
control whose output is based on the results of the previous printing. The
printer predicts the quantity of heat required to print dots and regulates the
electrical energy applied to the printhead. This prevents unevenness of print
density and results in the printing of narrow-ladder bar codes or vertical grid
lines that are straight from the microscopic viewpoint.