Flexible Packaging The benefits of UV LED curing systems in
Flexo printing By Robin McMillan, business development manager of narrow web and industrial Europe, Sun Chemical
D
ue to their lifespan, efficiency and multiple applications, light emitting diodes (LEDs) have
become ubiquitous - from their use in televisions to advertising signs and, more recently, in domestic lighting, having displaced incandescent and halogen lightbulbs. Within the packaging printing industry,
LEDs are also making their mark with UV LEDs being increasing adopted as an alternative light source for curing inks and coatings. UV LEDs offer a number of advantages over conventional UV curing lamps that result in production efficiencies, increased reliability and working life, reduced costs, higher quality print and, perhaps most importantly, fully-controllable and repeatable cure. However, to realise and enhance some of the benefits of using UV LED curing, specially formulated inks that use the latest technology are required. Specifically formulated UV LED curing inks maximise the benefits of UV LED curing systems by ensuring that the highest press speeds can be met, while delivering at least the same print quality and full repeatability, achieved with conventional UV curing systems. When manufacturing food safe or compliant packaging with UV curing inks, it is imperative that printers use Good Manufacturing Practice (GMP) techniques and, ideally, fully monitor the print process, including curing, throughout a production run. While monitoring UV curing through a production run has always been a challenge on narrow web presses and can remain so today, the use of UV LED can bring some peace of mind.
UV LED lamps operate at 100 per cent
intensity or very close to it (certainly greater than 90 per cent after 20,000 hours’ operation) for the life of the lamp (over 20,000 hours as opposed to 1,000 to 2,000 hours for a conventional UV lamp), whereas conventional UV lamps slowly decrease in intensity (at usable wavelengths) over the usable lamp life, with a proportion of the energy emitted shifting to unsuitable wavelengths for ink curing. A UV LED lamp also maintains its intensity and wavelength output (which is incidentally a very narrow wavelength band), ensuring there is no gradual reduction in the cure energy received by the uncured inks. Gradual cure reduction, almost impossible to control, is not obvious to
12 September 2019
consumption and heat generation. The lack of heat generation also means that thinner, more heat-sensitive substrates can be UV printed, delivering improved results on shrink sleeves, which inherently shrink and form better when thinner films are used. Unlike a 360 degree source such as a
a printer, but has knock-on effects in terms of the post-print performance of a label or package when tested for compliance or migration properties. Anything less than fully cured films may not meet migration limits, even if compliant inks are used. The longer and narrower wavelengths of LEDs suitable for print applications are also ideally suited for high filmweight and dense or opaque colours - as they penetrate the ink film further than wider and lower wavelength band light sources, they tend to cure from the bottom up. This ensures that even the most difficult-to-cure opaque, white or dense black inks can fully cure through the entire ink film, again minimising the risk of uncured material being able to migrate as well as ensuring good ink-to- substrate adhesion and excellent ink resistance properties. When a UV LED lamp delivers the UV
curing energy in a narrow wavelength band, very little energy is lost to wavelengths of UV light that have no benefit to the ink. This very efficient use of energy can consequently reduce curing times and increase print speeds, while lowering energy
conventional UV bulb, which requires reflector systems to focus the light onto a substrate, the design of UV LED lamps focuses all the light energy forward, minimising the size of lamp arrays and removing the need to keep reflectors clean and maintained. Additional benefits are improved health and safety conditions and environmental benefits from the absence of mercury, no UVB or UVC emissions and no ozone production. However, having specialist inks for specific curing techniques can result in a proliferation of products, which can be costly and require control to ensure that the correct products are used on specific jobs or equipment. For example, if a printer’s equipment portfolio is part conventional UV and part UV LED, they may need two different inks for the different curing systems in use (although many UV LED curing inks will cure under conventional UV curing lamps). Sun Chemical has an ideal solution to this challenge with the SolarVerse system, a range of colour base concentrates from which inks of differing characteristics and performance can be made as required on the printer’s shop floor. By simply blending a SolarVerse base concentrate with a specific technology varnish, a different, but ideally suited, finished ink is produced, ready for use on press in whatever colour specified. Whether the requirement is for compliant UV LED or non-compliant, conventional UV inks for sleeves or for inks for self-adhesive labels, all can be dispensed simply, easily and to order from the system. As the same SolarVerse base concentrates are used for each ink, colour consistency is also maintained regardless of the end print use. Then, as labelling and packaging applications evolve and new ink sets are required, it’s simply a question of upgrading the technology varnish to the appropriate product and dispensing the inks as needed, thereby ensuring full colour consistency, ink and press performance from a fully suited product.
sunchemical.com
convertermag.com
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