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Domino Printing Services
www.domino-printing.com
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Ink jet printing is a general name given to a family of non-impacting methods.
They all work by projecting drops of ink onto the surface to be printed.
This printing technology originated in the 1960s in America and Europe. It is
now in widespread use in various industries all over the world. The biggest
advantages of ink jet printing are its speed and its ability to print on
almost any type and shape of object. Although this technology is still advancing,
most of the physical principles involved were understood more than a century ago.
Ink jet printing makes use of acoustics, electrostatics and fluid dynamics.
It is, however, advances in computer science that have made ink jet printing
possible.
Several methods have been developed, but the two major ones are continuous and
drop-on-demand. We shall talk more about continuous ink jet, as it is the most
interesting and the one giving the highest printing speed. In this method, a
nozzle, which resembles a sophisticated spray gun, continuously emits a jet of
ink. Usually, this jet of ink would break into irregular and random droplets,
but in ink jet printing each droplet has the same size and flies through the air
with the same speed.
In order to print letters and small images, some means of selecting and moving
the droplets to the correct position on the surface of the object is required.
Domino achieves this by placing an electrical charge on the drops, using a
charging electrode. As the charged drop flies through the air it encounters a
plate with the same charge. This repels the droplet so that it can land at a
specified place on the substrate. As the charge on the drop effects how much we
deflect it, we have a method to control where to place our drops and what we can
print! The deflection of a drop is proportional to the voltage applied to the
charging electrode as the drop separates from the jet.
Usually the height of the printed letter is obtained by selecting several
successive drops. These are then charged and deflected, each one to a progressively
higher level. The width of the character is controlled by the speed of the surface
relative to that of the drops.
Ink jet printing is a very useful method of marking objects at very high speed,
without the need to touch or press on them. It can therefore print on the surfaces
that are delicate, such as the yolk of a freshly opened egg. It can mark oddly
shaped and irregular surfaces such as the curved bottom of a tin can, or the outer
surface of an orange. Printing speeds are very high. A single nozzle is capable of
producing 150,000 drops per second. It can print up to 2,000 characters per second
on surfaces running with a speed of nearly 5 m/s. To cope with this speed,
computer technology is used to control every single drop. A small computer is
used to continuously check the thickness of the ink, adjust the system pressure,
make several other automatic monitorings and sound the alarm if anything goes
wrong. The programme for this computer is stored in a microchip that is always
running while the printer is switched on. Because it has no need for disc drives,
tapes, keyboards, or screens, it is a very different type of computer to the ones
you may use at home or at school.
Ink jet printing is still progressing and developing. It has evolved very
considerably over the last twenty years and it is expected to become one of
the most widely used printing methods.
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