As with many labels in the digital printing field, the expression “single pass” applies to assorted print machine types, printheads and processes, all ranging from outsized web presses which print newspapers and their four-color, supplemental magazine and funny-paper sections, to commercial offset printers, and different types of inkjet single-pass print systems, including micro-electro-mechanical systems (MEMS) that in-line apply ink to media in a single, in-line, process. Single pass, in ordinary usage, means the media passes through the print device one time only. In most instances, the single-pass process draws media through several successive, but ganged print stations (“drums” in commercial print lingo), with each applying one color of ink (CMYK, generally) in a manner that produces a four-color print. Conventional large-format digital print devices employ a traveling printhead that moves in a transverse manner across the media. A wide-format, ganged inkjet MEMS system disposes of the travelling printhead, which significantly increases print speed while reducing the number of print device mechanisms (and build expense).
Once again, a formerly explicit term has become a label that identifies various machines and processes; thus, if you explore buying “single-pass” technology, ask your contact person to describe exactly what they mean by the term. For example, although single-pass usually describes a particular print process, it is also used to market the MEMS-type print-heads, which are described as an advanced technology that can produce print speeds of more than 10 times than that of traditional inkjet technology. This may be true, but a primary problem with super high-speed processing is in media handling, not high-speed ink application.
In addition, all large-format digital print processes that are suitable for signmaking must process adhesive-back vinyl, often in roll-to-roll systems. Unfortunately, roll-to-roll print media tends to “fly” when processed at speeds that run 10 times faster than traditional inkjet systems, which is why MEMS are usually found on flatbed printers. Therefore, even though MEMS-type printing can reach super speeds, it may not reach such velocity with all machines or media. Such characteristics do not take away from the value of MEMS technology, but they do add realism to the success claims.
An early view of digital print makers was that super-fast MEMS print systems would not match the image quality of conventional inkjet printing. Is this still true? When I have such questions, I call Heather Rockow, the energy curable business development executive for Kao Collins Inc. (Cincinnati), a maker of single-pass inks. Heather has strong experience in the ink and digital-print industry and, as well, has been my offstage inkjet ink consultant for more than 15 years. Heather said the original view was wrong. She said the newer, silicone-based MEMS heads produce excellent image quality. “If you buy scratch-off lottery tickets, those with all the bright and precisely printed colors and fonts, you’re buying single-pass, MEMS printed tickets,” she said. She also reminded me of popular large-format systems that comprise MEMS printheads.
WHAT ARE MEMS?
Micro-electro-mechanical systems (MEMS) are sometimes described as micro system technology (MST), but both comprise miniaturized mechanical and electro-mechanical elements made with microfabrication techniques (think nanotechnology) and design-engineered for processing and control mechanisms (i.e., micro-sensors and microactuators). Most MEMS printhead systems begin as inert, microfluidic structures, but in print systems, they’re often accompanied by silicon-based, piezo (compression) devices that fire high-voltage pulses at frequencies up to 100 kHz.Advertisement
Vince Cahill, president of VCE Solutions (Waynesboro, PA), a firm that consults with Fortune 500 and other companies, is a recognized ace on digital print systems and, like me, he believes readers should understand the central systems and processes before making print machine buying decisions. For example, Cahill separates inkjet components as ink, fluids, delivery systems, substrates, coatings, driver boards and software, but emphasizes that printheads are the central component. Printhead characteristics and capabilities determine the machine results – resolution, dot accuracy, speed, ink chemistry and viscosity. Regarding MEMS printheads, Cahill notes that interrelated MEMS manufacturing measures have enabled manufacturers to increase resolution, print speed and dot-placement accuracy which brings inkjet printer performance level with analog printing. Cahill says MEMS manufacturing processes intimately fabricate different appliances (and tiers) that are subsequently assembled into inkjet printheads. The MEMS building processes allow the production of densely packed systems – transistors, sensors and printheads – in submicron sizes of less than 500 nanometers (nm). Such packages are generally labeled as Nano-electro-mechanical systems. MEMS printheads, by the way, are appraised in nozzles per inch (npi).
Cahill says MEMS processes produce inkjet printheads with smaller features, less weight, greater precision and lower cost that other printhead manufacturing systems, which clearly predicts that MEMS printheads, in present or later amended forms, stand in the future of every digital imaging operation.
LARGE-FORMAT MEMS SYSTEMS
Several companies build single-pass MEMS printheads for installation in large-format digital print machines. As noted above, “single-pass” suggests that the media passes through the print machine one time, regardless of the number of inks applied. An example is Fujifilm Dimatix’s Samba and StarFire silicone-based MEMS printheads. The Samba features 2,048 individually addressable nozzles, 1,200-dpi native resolution and a native ink drop size of 2.4 pL that, the company said, can jet both UV-cure and aqueous inks. The single-pass feature arrives via the Samba scalability technology because its 1.7-in.-wide printheads are easily gang-arrayed to make a wide-span print bar. HP Scitex produces the XL2200 X2, silicone-based MEMS printhead designed for its HP Scitex FB7500/FB7600 printers that use UV-cure ink. HP said its X2 printhead incorporates silicon-based MEMS technology that features a combination of HP Scitex’s semiconductor manufacturing and piezoelectric inkjet technology. These industrial printheads operate in arrays up to 1,000 sets. HP said the FB7600, equipped with the X2 printheads, produces images at speeds up to 5,380 sq. ft./hr. The HP Scitex FB7500 UV-cure flatbed printer, equipped with the X2 printheads, produces high-quality POP/POS applications, exhibition graphics, signage, backlit displays and posters at speeds up to 5,380 sq. ft./hr.
The Xaar 1201 thin film, piezo, silicon MEMS printheads deliver eight gray levels at 600 npi to give an apparent resolution of 1,440 dpi, and can be configured to print four colors at 300 npi or one or two colors at 600 dpi. The speed and color agility depend on the price point and end-user profile that OEMs wish to target. The Xaar 1201 can jet dye-sublimation, eco-solvent, UV-cure or aqueous inks. The Xaar 5601 thin film piezo silicon MEMS technology features 5,600 nozzles and can jet up to 8L of fluid per hour. As noted above, modern MEMS printheads operate at speeds of more than 5,000 sq. ft./hr. – which, just for a comparative assessment, equals more than 3,500 A4 sheets an hour. Impressed? Get this; the research is ongoing.
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