Page 174 - Graphic Design and Print Production Fundamentals

162 Chapter 6. Imaging
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.

Types of Ink

Inkjet printing has become more advanced not only in the mechanics of how the print heads work, but
also in the variety and usage of different types of ink. Below are some common types of ink and a brief
explanation of how they might be used.

Aqueous Ink

Aqueous ink, as discussed earlier, is a water-based ink. This type of ink is used in consumer printers
using thermal technology, but can also be used in commercial piezo printers as well. Aqueous is well
suited to thermal technology because the formulation of the ink allows it to vaporize in the print head
for expulsion onto the paper. The water component of the ink, however, also contributes to its greatest
drawback: the susceptibility of the finished printed piece to run or smear if it gets wet. Many users of
desktop printers in their homes have been disappointed when they take their printed pages outside in the
rain. Even a few drops of water can cause the ink to run and bleed into the paper.

In commercial uses, aqueous inkjet is well known for colour fidelity and quality, but the finished piece
has to be protected from moisture. These types of print products would most likely only be used indoors,
mounted behind glass, or with a laminated plastic layer on top. There are water-resistant coatings that
can be sprayed onto a finished product, but even then, you would not want to leave it outside for an
extended period of time. Aqueous ink is a common choice for art prints.

Ultraviolet Inkjet

Ultraviolet (UV) ink is a type of energy-cured ink that stays wet until it is bombarded with ultraviolet
radiation. This UV radiation is commonly projected onto the freshly printed surface by means of a
special high-intensity light bulb. Once the UV rays hit the ink, a special molecular process is triggered,