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Developments in UV-LED Curing

(March 2012) posted on Tue Apr 10, 2012

The benefits of converting to UV-LED include reduced operating costs and energy consumption, lower emissions, increased safety, and more.


By Karla Witte

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The advantages of UV-LED for inkjet include: a smaller footprint for the unit, the instant on/off or adjustable capability, no generation of IR for the light source, and no generation of ozone. The intensity of UV LED can be altered, just like a dimmer switch at home. This capability allows print shops to add specialty details such as matte or gloss or special effects. And the visible-light-stability challenges are minimized as the ink is not readily exposed to light prior to curing.

As for screen printing, the advances in LED lamp technology and UV screen-printing ink formulations have proven LED curing as a viable alternative to medium-pressure mercury lamps. Chad Taggard, the VP of marketing for industry supplier Phoseon Technology, said recently that “printers using UV-curable inks should have units to measure the energy of any type of curing device.” This equipment will advise you to the amount of Watts and Joules that your ink/substrate achieves during exposure. A chemist then can create a formula that will cure based on this information. The print operator should then test the unit frequently to maintain the proper curing energy. It’s also important to use a testing device that works with UV LED, not just a UV device, because it would provide the wrong information.

Not long ago, UV screen inks could not be used with LED curing because they did not have the processing latitude to overcome the restrictions of using LED lamps. Restrictions included lower wattage and single-nanometer output.

The newest screen-ink technologies now formulate viable specialty inks that cure exceptionally well with 4- and 8-w LED 395-nm lamps at belt speeds of 30-120 ft/min. This curing-speed range relates to the ink’s color, the thickness of ink deposited, and the substrate color.

As for applications that best fit this type of curing, films truly suit LED because the LED projects very little heat towards the substrate. LEDs are lightweight when mounted to the carriage, which is why smaller digital printers use LED. UV-LED lamps work well with any applications where the curing system can be within 25 mm of the curing substrate.

Initial research has already shown that 365-nm UV provides better surface curing in a dark colored flexo ink, while having inferior cure at the print surface. Adding the higher energy output 385-nm UV-LED light source inline with the 365-nm light source had positive effects on the ink surface and substrate interface for curing (Figure 1). The belief is that as higher output UV-LED light sources are developed, the cure deficiencies may be overcome in the single-peak-irradiance-wavelength systems.

Other ink developments include research into studying the impact of lack of IR heat on the curing process with UV LED and looking at how single-wavelength UV light may impact the overall adhesion of ink to a variety of substrates. Studies also are underway on the potential of photoinitiators specifically formulated to optimize curing with the UV-LED wavelengths, noting that getting regulatory approval on novel chemistries requires long-term development.

Looking at the bottom line
Overall, the market is starting to see the addition of practical lamps and inks. The benefits of converting to LED curing are numerous, including the reduction of operating costs, reduced emissions, and the use of mercury bulbs, as well as increased safety and a huge reduction in energy usage. It’s important to note that LED costs more than mercury-lamp systems. The up-side here is the consumable costs are eliminated, and so is the expense for blowers, ballasts, and other peripherals.

If considering an investment in UV-LED curing, first prepare an ROI assessment to justify the cost of making a switch to LED from other curing types. Operating costs are significantly lower with UV LED. UV LED can be turned on or off instantly with no warm up time required. Printers who take advantage of this can significantly reduce their operating costs.

Printers also need to keep in mind that thinner and/or heat-sensitive substrates can be used with UV LED. Not only does this open the doors to potential new revenue streams, but it also reduces shipping and storage costs. It is possible that a print shop might save 30 % on shipping costs alone.

Karla Witte is the VP of product development for INX Digital Int’l Co.She has been involved in digital printing of fine and graphic art for 19 years and has also worked for Harvest Productions/BullDog Products.She can be contacted at karla.witte@inxdigital.com.
 


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