Mercury vapour lamp technology has been around since 1880. Today, mercury lamps are inside most UV curable wide format inkjet printers. One of the major disadvantages of mercury lamp technology is the broad range of wavelengths they emit, including a lot of infrared — and therefore: heat.
Although you could theoretically keep refining this old technology, that wouldn’t be future proof. A printer manufacturer that would invest in improving mercury lamp technology would show little understanding of environmentally sound development strategies. Not only do mercury lamps contain highly toxic mercury (a problem at the lamp’s end of life), they may also generate ozone (a problem in usage). But what may tilt the scales entirely against this UV curing technology is that it keeps printers from broadening their capabilities.
The alternative to the mercury UV curing lamp is the UV LED lamp. LEDs don’t emit ozone at all and they are completely mercury free. But more importantly, they enable printers to experiment with materials that normally aren’t suitable to be printed on with UV curable inks and thus dramatically expand the range of applications they can offer to customers.
LED arrays as found in UV LED curable wide format inkjet printers allow for faster finishing of jobs. A printer like the Durst UV Omega 2 allows for much faster operation than comparable mercury lamp based printers because there is no lamp warm-up time and no shutter open/close delay. UV LEDs are turned on only when they’re actually over the substrate and that typically takes only a couple of milliseconds.
Other advantages are: no stray light and big power savings. In fact, LED technology may reduce a printer’s power bill by up to 80% — with Durst claiming 65% reductions from using the UV Omega 2 because of the air-cooled 395nm-wavelength LED lamps the printer uses.
Advanced UV LED curing capabilities
The “instant ON/OFF” feature as used in all areas of curing can achieve matte or gloss finishing with specially UV LED formulated inks. Outside the printing business, the granular control over LED lamps gives coatings and adhesives unique properties.
Those who discuss whether UV LED curing is environmentally sustainable often state that UV LED curing inks are more toxic than others used in the printing industry. This, I found, is wrong. It’s true the narrow UV-A wavelength of most UV LEDs necessitates the use of inks that are formulated specifically for UV LED curing. But it’s untrue these inks are all less healthy to handle and use than others, or less environment-friendly for that matter.
FlintGroup manufactures EkoCure inks. They partnered with Phoseon Technology for the development of EkoCure inks — which, as the name suggests, are eco-friendly. Polymeric Imaging developed the Twilight LED ink system that works with 365/395nm LEDs, is eco-friendly and remains durable when used outdoors for up to three (3) years. The company says Twilight LED inks are extremely bright and saturated.
Agfa has the :Agora ink system. These inks give users low odour, solvent-free inks that can be applied in one pass. :Agora inks are the only UV inks that are curable by LED light at all available wavelengths and come with a 12-month shelf life from the date of manufacture. The ink pigments have been carefully selected to have good balance for outdoor light fastness with a huge colour gamut.
Pelikan too has UV LED curable inks. Then there’s Tritron with a complete range of ink products for inkjets.
Another German ink manufacturer, Ruco, has a Series 900UV-LED ink system for screen printing that are completely free from toxic solvents and comply with EN71, a European directive for the safety of toys (more specifically, the migration of certain elements). Coates has a heavy metal free ink mixing system for screen.
SunChemical develops JetStream for Xaar heads and UV LED curing. Nazdar has specially formulated inks for UV LED curing that work with 395/405nm 4/8W lamps with the lamp at a distance of less then 4mm from the substrate.
Marabu, Siegwerk and Ruco have low migration inks for the screen printing industry. Jänecke & Schneemann have special UV-LED curable inks for offset printing with UV LEDs. Ruco even has inks that are UV LED curable on glass bottles.
The use of specialty inks and less heat generated by the LED array passing over the substrate allows you to print a range of materials you couldn’t print before (or you would need more expensive printing technology for). As a result, in the advanced UV LED printing capabilities department we find printing on bubble wrap, athletic tape, shrink wrap (!), thinner heat-sensitive styrenes, and everything from foils and laminates, to coated paper, PET, industrial film, PVC, PE, PP, BOPP, folding carton to very heavy stocks and glass.
Better quality and higher return on investment
But UV LED will also protect your investment better. A mercury lamp will typically run for 1500 – 2000 hours. The quality of the radiated UV and the curing capabilities will deteriorate faster. Both the reflector condition and age of the bulb will determine the quality of the lamp and whether it’s still fit for UV curing. The lamps themselves aren’t very expensive, but if you add the environmental challenges that come with the disposal of the mercury inside the lamp, the replacement costs a lot more than what you actually pay for a new one.
The biggest manufacturer of LED lamps in the industry, Phoseon Technology, specifies an expected life time of over 20.000 hours of on-time for their UV LED light sources. Given that LEDs are only switched on if they are actually over the substrate curing, the lifetime should exceed the lifetime of a printer.
Phoseon Technology says it can claim this as they have a large number of units in the field for years. Additionally, they constantly have more than 50 light sources in life time testing in their labs, some under odd conditions — for example air exhausts closed on some air cooled units, so they almost can’t breathe.
However, Phoseon Technology’s Dirk Exner does stress the fact that for the lifetime of UV LED light sources, proper control of LEDs, as well as proper cooling are crucial. “Phoseon uses proprietary technology to accommodate for this. In the meantime, Phoseon has well over 100 patents and patent applications in that field,” he says.
Another important aspect when using air cooled lamps is ink mist. Exner: “At least Phoseon products are internally protected and sealed, so ink mist has no impact on performance or life time.”
A longer lifetime, up to 80% less power consumption and environmentally less costly technology all cater for a better investment in more than one sense of the word.