ATM, vending machines receipts, bus ticket,
use thermal printing. . It is based on the principle of thermochromism, a process of change in colour
with heating. It works by creating
impressions using print-heads over a special kind of paper roll coated with
organic dyes, waxes. The paper used is a special thermal paper that is
impregnated with mixture of a dye, a matrix such as a fluoran leuco dye and an
octadecylphosphonic acid. When the print-head made of regular array of
minuscule heating elements receives the signal for printing, it raises the
temperature to the melting point of the organic coating to cause print
impression on the paper through the process of thermochromism. Usually
black-colour print-outs are taken but
red print-outs can also be taken by controlling the temperature of print
heads. However, when the thermochromic paper is exposed to heat or
unattended in person’s pockets, it darkens the paper, hence fade the original printing
marks on it.
