The future's bright

Simon Eccles
Friday, July 5, 2013

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?

Snow in May and torrential rain in June – the spring and summer of 2013 have not been thus far, for most people, all about the UV rays. Unless they’re involved in print that is.

Here, browsers of new technologies rolled out at Sign and Digital UK and Fespa, will have spotted a shift. 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.

Cool 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.

Also at Fespa, Integration Technology (ITL) – an Oxfordshire manufacturer that has been making UV lamps for printers since 2000, starting with mercury and introducing LEDs by 2004 – showed its new MZero LED lamp for large-format inkjet with travelling carriage head units. These can be fitted as a straight swap for the firm’s existing MZero mercury heads that are already used in existing printers (DYSS is one user mentioned by ITL).

The mountings and electrical connectors are identical, so no major redevelopment is necessary other than sourcing an LED compatible ink, says managing director Adrian Lockwood. He also reckons that the energy output and price is comparable to the mercury lamps too, making the conversion attractive to existing users.

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."

Vutek, now owned by EFI, was an early adopter of UV curing, using mercury lamps in its PressVu flatbeds a decade ago. But it is now adopting LEDs wherever practicable, says Mark Goodearl, product manager for the roll-to-roll printers. "Our GS and HS range both have LEDs. The frustrations used to be with substrates that didn’t behave well under the heat of a mercury arc lamp. Moving to LEDs is a way of reducing the heat. The advantages to the customers are too great to ignore, and we plan to put LEDs on every printer we can," he says.

In this last statement, however, is an obvious caveat. Goodearl qualifies that, though the LED and mercury vapour versions of the GS family run at the same speeds, LEDs are not yet suitable for all applications. "Not everything is suitable for LEDs yet, especially for the higher-speed printers," he says. "We have to prioritise which of our models to redesign for LED, which is no small project."

An example of the current limitations of LED curing, is EFI’s fastest flatbed, the 3.2m-wide HS 100 Pro, introduced at Drupa last year. EFI believes itself to be the only manufacturer so far to use LEDs on superwide printers (classed as 3m and wider), but the HS 100 Pro in fact uses a hybrid UV curing system that combines LEDs and mercury lamps. The LEDs are mounted on the head carriage and immediately ‘pin’ the ink, partly curing it to keep the dots sharp without running. The more powerful mercury lamps then initiate the full cure.

More to do

So while use of LED-cured UV is on the rise, not every manufacturer is convinced currently of its superiority in all scenarios. Inca Digital and Durst, which like EFI offer very fast UV flatbeds to print display graphics on rigid sheets, still use mercury lamps for performance and cost reasons.

Until LED lamp technology improves still further, there will only be so much the ink manufacturers can do to ensure the result is as fast drying and durable as if the print had been cured by mercury, explains Tudor Morgan, European group marketing manager at Fujifilm Speciality Inks.

"It’s much easier to get inks with the required flexibility, vibrancy and adhesion with mercury lamps, because the choice of raw materials is much greater," he says. "When you look at LED, the benefit is environmental – low energy, lower temperature, low emissions, a whole range of things. But what LEDs don’t yet offer from the ink point of view is productivity, speed and adhesion that’s the same as mercury."

Peter Saunders, business manager for digital at Sun Chemical, agrees. Mercury lamps still "close" the ink surface quicker than LEDs, he says, so print is touch-dry immediately. "With fast printers from Durst, Inca, etc, especially with board stackers, you still need mercury lamps to prevent set-off," he says.

Saunders is, however, confident that neither LED lamps nor ink technology have yet developed as far as they’re going to. "LEDs have improved a lot in the past 18 months. It’s certainly much easier to formulate inks for LEDs than two years ago. It’s clear that more powerful LEDs will be developed in future, while costs will fall as quantities and yields rise," he says.

"Even if LED technology were to stop where it is now, we would still be able to improve our inks over time as we are still doing for mercury. But as LEDs do improve, it will definitely help the performance of our inks," he adds.

The consensus seems to be, then, that use of LED curing in wide-format print is still on the rise. Certainly, with the likes of Inca Digital and Durst still not convinced it’s a viable option for their purposes, it has by no means replaced mercury vapour for high-speed, fast drying and superwide-format print. But a quick appraisal of where the lamp and ink technology was at five years ago, provides an exciting insight into where it might be in five years more.


Mercury vapour vs LEDs

Medium-pressure mercury vapour lamps are widely used. They produce a wide range of ultra-violet wavelengths, but also a lot of infra red, which is radiant heat. The problem of ozone generation has largely been overcome. They work by striking an electrical arc through a glass tube filled with nitrogen and vapourised mercury. They need a lot of power and run very hot - between 600°C to 800°C internally. They cannot be switched on or off quickly. Output degrades over time, typically needing replacement after 1,000 operating hours. Old lamps need to be disposed of in line with environmental regulations.

Light-emitting diodes (LEDs) are solid-state components that are widely used in modern lighting applications. The UV type are just more specialised and expensive. They are used in multiple arrays in curing lamps. They produce relatively limited wavelengths of UV so the inks need to be tuned to match. UV LEDs don’t emit IR so the print media doesn’t heat up much, but the arrays still need to be air- or water-cooled. They use far less power than mercury lamps, and only degrade very slowly. LEDs can be switched on and off rapidly, or varied in intensity, without damage. As they are only switched on when needed, their lifetime can be extended to years, potentially the lifetime of the printer.


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