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Printing Processes

Part Two: Inkjet Printing


Inkjet

Epson Inkjet Printer

DVD/CD Inkjet printers use liquid inks to create printed images by spraying droplets of ink onto the paper or discs. The basic idea is simple; squirt a droplet of ink in the appropriate area to create text and images. In reality the process is more sophisticated than it sounds, mostly because these droplets of ink are measured in Pico liters (or one trillionth of a liter). That is small, I mean really small, in fact it would take 591,470,593,750 Pico liters just to make a 20 fl oz. (591 ml) Venti Cappuccino from Starbucks. Another reason this process is sophisticated is the droplets must be placed within 5/10,000th of an inch of its intended location. All of that must be done in 1/5000th of a second.

Today’s inkjet printers can accurately lay down 14,400,000 droplets per second. This technology is taken for granted now but the development took decades. In the development two roads diverged, one marked “Thermal Inkjet” and the other marked “Piezoelectric”.

Thermal Inkjet

Not to be confused with thermal transfer printing, gets its name from the 400+ tiny nozzles with a heating element that is instantly heated to over 400ºC causing a tiny steam explosion that propels the ink out of the nozzle. They are also known as Bubble Jet. They get their name from the bubble that pushes the ink out of the cartridge caused by the tiny steam explosion; the name was trademarked by Canon in 1985.

Piezoelectric

It is called Piezoelectric because it uses a piece of piezoelectric crystal to control the flow of ink to the nozzle. Piezoelectric crystals generate an electric voltage when deformed, similar to the ignite button on a gas grill. They also deform when an electric voltage is applied, like in a quartz clock or wristwatch. It was these everyday items that led to the development of the piezoelectric inkjet.

Piexoelectric Ink Cartridge

The print heads of one of these printers contain hundreds of tiny nozzles, each with a piezoelectric crystal. When voltage is applied to the crystal it changes shape, causing the ink to be squirted out the nozzle. Epson’s patented Micro Piezo technology allows droplet size to be controlled by the printer between 1.5 Pico liters and 10 Pico liters.