aNewDomain.net — Mercury vapor lamp technology has been around since 1880. These days, mercury lamps are inside most UV curable wide format inkjet printers. But there’s an alternative. It’s based around the Mercury-free, low-power, no-ozone-ever UV LED lamp curing tech. Our Erik Vlietinck digs in.
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, it wouldn’t be future proof.
Not only do mercury lamps contain highly toxic mercury — a problem at the lamp’s end of life — but they may also generate ozone, a usage problem.
The alternative to the mercury UV curing lamp has been the UV LED lamp, which has now been available for a couple of years. LEDs don’t emit ozone at all and they are completely mercury free. Other advantages are no stray light and big power savings.
In fact, LED technology might reduce a printer’s power bill by up to 80 percent.
The instant ON/OFF feature of LEDs enable printers to achieve matte or gloss finishing with specially UV LED formulated inks.
Until recently, these inks were believed to be more toxic for the environment than mercury lamp curable UV inks.
This is rapidly changing as UV LED printing is picking up. Most printers buy a UV LED curing wide format inkjet because they can use the “green” label in their marketing efforts. But so far they remained silent about the inks they had to use.
That’s all changing
Recently, FlintGroup partnered with Phoseon Technology for the development of EkoCure inks. As the name suggests, these inks are eco-friendly. Polymeric Imaging developed the Twilight LED ink system that works with 365/395nm LEDs. The ink is eco-friendly and remains durable when used outdoors for up to three years.
German ink manufacturer Ruco has a Series 900UV-LED ink system for screen printing of which the inks 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 UV LED screen printing.
Siegwerk has launched Sicura ECO, a UV flexographic ink series made from more than 50 percent plant based constituents. They’re avoiding raw material which could be used for the production of food.
How far printers can take the “green label” is shown by German converter RAKO, who won a major award last year for its use of Sicura ECO inks with cellulose-based linerless labels (made from 90 percent renewable raw materials), plus a hotmelt adhesive produced on a 70 percent renewable raw material basis.
The use of UV LED technology allows printing on a range of materials you couldn’t use before. As a result, printers can now print on bubble wrap, athletic tape, shrink wrap, thinner heat-sensitive styrenes, foils and laminates, coated paper, PET, industrial film, PVC and even glass. As all of the eco-friendly inks are defined as ‘low migration’, direct printing on food packaging is possible too.
Some additives, which are added to printing ink formulations, can migrate. These include flow additives, flexibilisers, surface treatments on pigments, dispersing agents and photoinitiators.
The most harmful component of UV curable inks seems to be the photoinitiator. I found the best general explanation of what a photoinitiator is at BASF. In a nutshell, it’s a chemical component that enables polymerization. It binds the ink to the substrate.
In 2005, ITX, a photoinitiator used in UV curable inks formulated for mercury lamps was found in a packaged milk substitute. Due to a lack of information and readily available toxicological data, ITX was subsequently ‘banned’. The migration of this substance from the packaging material into the packed foodstuff was seen as alarming.
However, everything in any ink or coating with a molecular weight under 1000 Daltons can potentially migrate. Materials with a molecular weight above 1000 Daltons can migrate too, but they pose no risk to human health as they pass directly through the body.
Of course, UV LED technology by itself has more ‘green’ features. For example, 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 determine whether the lamp still fit for UV curing. The disposal of the lamps is expensive because of the environmental challenges posed by the mercury inside.
The biggest manufacturer of LED lamps in the industry, US-American 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.
For the lifetime of the UV LED lamp, a proper control of the LEDs as well as cooling are crucial. The manufacturer has to build these into the array and Phoseon as well over 100 patents in this area of expertise.
A longer lifetime, up to 80% less power consumption and environmentally less costly consumables that are more healthy to handle all cater for UV LED curing to be the future of inkjet printing on an industrial scale.