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The Future's Bright

LED technology is developing fast and is now an option in a number of applications that could previously only be handled by arc lamps - a trend that is set to continue. So is it time to ditch the mercury?

Thanks to wide-format inkjets with powerful light-emitting diode (LED) curing lamps, together with developments in ink compatibility, ultra violet-cured print has broken out of its ‘traditional’ role in packaging,  labels and non-absorbent rigid media. Now  it’s winning users in  niche or personalised sign, display and decorative print, too.

The question is, of course, to what extent LED technology is replacing, and will replace, the mercury vapour (also called arc) curing lamps that have been the standard feature of inkjet flatbeds since they first appeared in the  early 2000s.

"The power of LEDs in terms of radiance and energy density or dose, is increasing dramatically."
Chad Taggart, Vice-president of Marketing and Development, Phoseon Technology

Certainly LED curing offers some significant advantages over mercury vapour. Because it runs much cooler than mercury, it is an enabling technology that gives relatively small sign shops a versatile and fairly ‘green’ alternative to eco-solvent inks for a wide range of media. And while earlier LEDs were not powerful enough to replace the older mercury vapour arc lamps for the highest speed inkjet printers, this seems set to change.

"LED UV is perfect for roll printers, such as the Fujifilm Acuity 1600 LED, Roland 640 LEJ or lots of other printers where LED has enabled UV to go into the large-format area where it wasn’t before," explains Gary Barnes, global product manager at Fujifilm Speciality Ink Systems. "When people get to the end of what they can achieve with eco-solvent, UV lets them add a bit more, such as white ink or clear inks, to add value to their work. The big   benefit is that LED is cool, so you can use it with all of the roll media without issues of heat, such as distortion,   that  would happen with medium-pressure mercury lamps."

Mimaki, one of earliest adopters of the technology, is another advocate of LED. At Fespa the vendor showed production versions of a pair of large-format printers, both using the same printheads and LED curing lamps, that offer very respectable speeds. The JFX500-2131 flatbed gives "usable production quality" imaging with white ink at up to 70sqm/hr, which has been about the upper limit for LED printers to date. The even faster 1.6m-wide UJV500-160 allows production quality at 100sqm/hr.

Another UV lamp maker, Phoseon in the US, concentrates on LEDs. It has just announced its FireJet FJ200 air cooled LED head in five sizes for inkjets, which emits 12W/sqcm. Its most powerful lamp is the larger water- cooled 16W/sqcm FirePower.

"The power of LEDs in terms of radiance and energy density or dose, is increasing dramatically," says Chad Taggart, vice-president of marketing and development. "Every two to three years, we’re doubling the output capability. For instance we went from 4W/sqcm in 2008 to 8W/sqcm in 2010, to 16W/sqcm in 2012. There’s no reason it can’t hit 24W/sqcm or more in future.

"We believe that the perception of low power is from people not staying up-to-date with our technology. We have many customers in large-format today using LEDs for the highest speeds available. Some printers are air-cooled, some are water-cooled. Typically our highest powered products are water-cooled. If you keep the LEDs cooled properly they’ll last 20,000 or 30,000 hours."

LEDs also allow new applications to be developed, Taggart points out. "There are elements that you cannot do with mercury. You can turn LEDs on and off instantaneously, but not with mercury. If you have a job with opaque white you can increase the intensity of LEDs."