InkJet technology explained . . . .

Over the last several years most of the major vendors have introduced new high speed inkjet printers. At IPEX and Graph Expo 2010 inkjet technology was seemingly everywhere. Wherever you turned someone was talking about their new inkjet technology. So what is it actually and how do you tell the differences?

First of all the technology is not all that new. The concept of inkjet printing originated in the 19th century, and the technology was first developed in the early 1950s.  Starting in the late 1970s inkjet printers that could reproduce digital images generated by computers were developed, mainly by Epson, HP, and Canon. Today, solutions are available from a large variety of vendors including, HP, InfoPrint, Kodak, Oce, Xerox and others.

There are two main technologies in use in production inkjet printers: Continuous (CIJ) and Drop-on-Demand (DOD). Continuous inkjet (CIJ) heads fire a continuous stream of electrically charged ink droplets at the paper. Drop-on-Demand (DOD) heads fire ink droplets as needed, targeting specific spots on the media. Drop-on-demand heads are flexible enough to accommodate three different print technologies.

Thermal inkjet (TIJ) –HP is  TIJ’s leading advocate as this technology is incorporated in the T350 / T300 and the new T200 inkjet web presses. Only real downside is that TIJ cannot print on a coated stock. For now, HP requires either specially treated papers, or use of a “bonding agent” that limits ink penetration into the page, minimizes dot gain and helps to ensure ink adhesion.

Piezoelectric heads have been a mainstay of inkjet printing for 25 years. Piezo crystals are electrically charged creating a vibration that causes the ink out of the nozzle. Piezo heads can accommodate a wider variety of inks than TIJ or CIJ heads and, although more expensive, are much more durable. This is the most common technology used by the various vendors today.

Phase Change is something completely different. Solid ink—a polymeric resin—is rapidly melted and fired through a nozzle. The sudden heating and melting causes a molecular change in the resin, which leaves the nozzle as a liquid, but returns almost instantly to a solid as it hits the printing media.

The types of colorant or inks utilized by the different technologies can have a big impact on the output. The majority of solutions use aqueous inks based on a mixture of water, glycol and dyes or pigments. CIJ and DOD can have ink formulations based on Pigments and Dyes. Pigment based inks are typically more expensive offer the best combination of color longevity and gamut. Dye based inks are usually less expensive and fade rapidly when exposed to light.

The substrates or papers that are used are also an important consideration when evaluating various inkjet technologies. Because the ink used in most inkjets is water-soluble, care must be taken with inkjet-printed documents. Lightweight papers and coated stocks can present challenges.

Although inkjet vendors are touting the various virtues that this technology can offer, it is important to conduct a thorough analysis of all the alternatives. Yes the promise of raw speed, duty cycles, web width, and very aggressive TCO’s is enticing but make sure to consider all factors.  Consider the variability in performance, the overall systems productivity, post processing requirements, drying times and substrate flexibility. All these factors are important and should be considered before investing in an inkjet solution.

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