How Inkjet Printing Works
There are three main steps to producing a
drop with thermal technology. First, the chamber holding the
ink bubble is heated. Second, the bubble bursts due to heat
and the ink drop shoots out of the nozzle. Finally, the
vacuum from the drop leaving the chamber draws the next
bubble into the chamber. There are between 300 and 600
nozzles per print head, all of which can fire at the same
time. "These deliver drop volumes of around 8 - 10
[picoliters] (a [picoliter] is a million
millionth of a [liter]), and dot sizes of between 50
and 60 microns in diameter." Thirty microns is the smallest
dot size visible to the naked eye (Anderson,
1999).
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Four to eight of these tiny drops are fired onto the paper to make a color dot. Larger dots of 35 picoliters are usually created with black inks. Part of this difference is that the colors are usually created with dye based ink and the black ink is a pigment based ink (Anderson, 1999). Dye based inks produce a wide range of very vibrant colors whereas pigment based inks are more durable and water-resistant (ENCAD, 2000). Pigment based inks also have larger molecules (Anderson, 1999) because they are particles suspended in solution (ENCAD, 2000). Because thermal technology uses heat to create the drop, all the inks used must be heat resistant. This narrows the selection of inks and their characteristics such as water-resistance (Anderson, 1999).
Another drawback of thermal technology is drop control. Thermal technology produced drops are shaped like a teardrop with a long tail that can break off and produce several smaller, uncontrolled droplets. This effect is called misting and is undesired (Rand, 1996). It also takes more energy and time to print with thermal technology because of the heating and associated cooling time (Anderson, 1999).
Piezoelectric technology refers to the
electric component, called a piezoelectric crystal, that is
used to create the mechanical motion to push the drop out.
Whenever a drip is required, an electrical current is sent
through the crystal which causes it to flex and push the ink
out of the nozzle (Anderson, 1999). Epson is the primary
producer of inkjet printers with piezoelectric
technology.
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With the early piezoelectric technology printers, the print heads were very big and required a lot of voltage. New technology has allowed Epson to replace the large component with a smaller one that is made of layers of ceramic and piezoelectric crystal. This new component is called a multi-layer actuator and not only uses less electricity and is smaller, but produces 100 times the force as the old version (Rand, 1996).
One of the biggest advantages of piezoelectric technology is the drop control. Because the firing is controlled electrically, drop size, speed, and force can be precisely controlled. In addition, instead of producing a tear drop shape, piezoelectrically produced dots are perfectly round so there is no misting. This creates a much higher quality print. These printers can also print faster because there is no cooling time (Rand, 1996).
Another major advantage of piezoelectric technology is the flexibility in choosing inks. Unlike thermal technology, there is no requirement that the ink be heat resistant so manufacturers can focus on other characteristics of the ink. Black ink tends to penetrate the page instead of spreading out on the surface but is slower to dry. Color inks dry quickly so that there is no blurring (Anderson, 1999). Other characteristics that printers consider are the print medium, or substrate, and resistance to water and ultraviolet light (ENCAD, 2000).
© 2000, Patricia Watson