In the thermal inkjet process, the print cartridges contain a series of
tiny chambers, each containing a heater, all of which are constructed by
photolithography.
To eject a droplet from each chamber, a pulse of current is passed
through the heating element causing a rapid vaporization of the ink in
the chamber to form a bubble, which causes a large pressure increase,
propelling a droplet of ink onto the paper (hence Canon's trade name of
Bubble Jet). The ink's
surface tension,
as well as the condensation and thus contraction of the vapor bubble,
pulls a further charge of ink into the chamber through a narrow channel
attached to an ink reservoir. The inks used are usually water-based and
use either
pigments or
dyes
as the colorant. The inks used must have a volatile component to form
the vapor bubble, otherwise droplet ejection cannot occur. As no special
materials are required, the print head is generally cheaper to produce
than in other inkjet technologies.
Most commercial and industrial inkjet printers and some consumer printers (those produced by
Epson and
Brother Industries) use a
piezoelectric material
in an ink-filled chamber behind each nozzle instead of a heating
element. When a voltage is applied, the piezoelectric material changes
shape, which generates a pressure pulse in the fluid forcing a droplet
of ink from the nozzle. Piezoelectric (also called Piezo) inkjet allows a
wider variety of inks than thermal inkjet as there is no requirement
for a volatile component, and no issue with kogation (buildup of ink
residue), but the print heads are more expensive to manufacture due to
the use of piezoelectric material (usually PZT,
lead zirconium titanate).
A DOD process uses software that directs the heads to apply between
zero to eight droplets of ink per dot, only where needed. Piezo inkjet
technology is often used on production lines to mark products. For
instance, the "use-before" date is often applied to products with this
technique; in this application the head is stationary and the product
moves past. Requirements of this application are high speed, a long
service life, a relatively large gap between the print head and the
substrate, and low operating cost.
No one writes any more … http://www.ctheory.net/articles.aspx?id=74