Page 173 - Graphic Design and Print Production Fundamentals

6.2 Inkjet

Roberto Medeiros

Inkjet printing is a type of digital imaging where drops of ink are jetted onto the substrate in a very
precise pattern from a nozzle. This nozzle, also called the print head, is required to be very precise and
accurate, which is a challenge when you consider that the goal is to get many thousands of tiny drops
of ink to land exactly where needed on the printed surface. Over time, inkjet technology has become
more advanced, allowing greater resolution, more accurate colour, and overall, finer visual fidelity to the
original. The most common method of inkjet printing for commercial purposes is called drop-on-demand
(DOD). This type of inkjet print head only fires each individual droplet of ink when needed (on demand)
and comes in two types, thermal or piezoelectric (see Figure 6.1). Accuracy in DOD inkjet printing is
achieved by keeping the print head close to the surface being printed (substrate) as the velocity of the
jetted ink is low.

Figure 6.1 Piezoelectric head on the left,
thermal on the right

Thermal Inkjet

In a thermal print head, each nozzle contains a special reservoir that is bounded by a heating element.
When current is passed through the heating element, it causes the ink to expand rapidly, ejecting out of
the nozzle to land on the substrate in a given position. The print head is made up of a matrix of many of
these chambers, and each print head is connected to a different colour of ink. As the ejected ink leaves
the chamber, fresh ink is drawn into the reservoir by surface tension and the vacuum created by the
previous drop of ink leaving.

Thermal inkjet is most common in household and consumer grade inkjet printers. A major benefit to
using thermal printhead technology is the relatively inexpensive print head. Since each colour printed
requires a separate print head, and some print devices can contain eight or more colours of ink, thermal

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