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 technology keeps the initial cost of the device low and reduces replacement costs when a print head fails, or is damaged.

Piezoelectric Inkjet

Piezoelectric (piezo) print heads also use a tiny reservoir to hold a droplet of ink. However, unlike thermal printheads, piezo heads contain a small flexible membrane, or diaphragm, that moves up and down to squirt the ink out of the print nozzle. The pressure caused by the flexing of the piezo material is very precise, allowing a drop, or multiple drops, to strike the substrate accurately. Similar to thermal, the print head is made up of a matrix of a number of these individual nozzles. And by using multiple print heads, multiple colours are possible.

Piezoelectric is more common in commercial and large-format printing applications, although there are a few consumer grades of printers that use piezo as well. Piezo is more accurate, and because the ink in the chamber doesn’t have to be vaporized to form the droplets of ink, piezo can print with a wider variety of inks such as aqueous, ultraviolet, and latex.