Sign & Digital Graphics

July '17

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42 • July 2017 • S I G N & D I G I T A L G R A P H I C S DIGITAL PRINTING AND FINISHING DIGITAL GRAPHICS Piezo & Thermal Inkjet Technology The two most common printhead systems in today's inkjet printers employ either thermal technology or piezoelec- tric technology. Piezoelectric printhead technology, which was first introduced by Epson in 1964, employs piezo-ceramic crystals at the rear of each printhead ink reservoir. When an image file is RIPed and elec- tronic data is sent to the printheads, an electric charge excites the piezo crystals causing them to expand and contract at very specific frequencies. The pulsing of the crystals drives ink in the printhead reservoir so that a tiny droplet of ink fires out of the nozzle and onto the substrate, (see Figure 4). Piezoelectric printheads are quite durable, are used in a wide vari- ety of inkjet printers, and can accept a wide variety of ink types. Thermal inkjet technology—used only with aqueous-based ink systems— employs heat behind the ink reservoir in the printhead. A RIPed file sends the data to the printheads causing a pulse of heat that in turn forms a tiny bubble in the ink chamber. The bubble fires an ink droplet out of the nozzle and onto the substrate, (see Figure 5). Both thermal- and piezo-based inkjet printers can generate professional-qual- ity, high-resolution large-format images. Some photo print shops use archival aqueous inks that have proven to be bet- ter than the standard ink for long-term durability. Archival inks are humidity and light resistant and claim to last for as much as a century rather than fading over time. They have a protective resin coating that increases durability and an impressive color gamut keeps photos true to the original image. Aqueous Ink: Dye vs. Pigment Both thermal and piezo inkjet print- heads can deposit aqueous (water-based) inks. The term "water-based" is an indus- try-accepted misnomer. The colorant is actually suspended in a neutral carrier solution that may be water or a soy-based liquid. Generally aqueous prints are used Piezoelectric Inkjet Figure 4: Piezoelectric ink distribution vibrates ink onto the surface. Thermal Inkjet Figure 5: A thermal inkjet printer uses a heating element to distribute ink.

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