Flexo Technology
RUNNING FLEXO FAST & CLEAN
By Tom Kerchiss, chairman of RK Print Coat Instruments Ltd S
ome would say that for converters who print that there has never been, at least in terms of technology, a better time to be a practitioner of print, especially for those who are flexible packaging providers, narrow web label printers and producers of folding carton and other packaging related processes. Greater levels of automation and faster processing speeds certainly sound good. Faster press speeds means that the faster a new job can be mounted, printed, dried, and shipped out the door, the sooner the next job can be introduced, mounted and the whole process begins again, therefore increasing profit. Flexography, not known for being a process that sits it out on the side-lines, has enjoyed more than its fair share of productivity enhancements and innovation in recent times. Replacing gears with servo-driven technology has provided the responsiveness and precision needed for web handling and tension control when running thin label stock and filmic materials for shrink wrap or other heat sensitive materials, for example. Challenges exist though; ‘Running Clean,’ using less ozone depleting materials, as well as water based and synthetic formulae, are becoming the order of the day. Mono-filmic, bio-compostable and various natural polymers may be used to meet ever stricter environmental and sustainability requirements. Nevertheless, some things remain the same. Consistent results in flexo tend to be dependent on how much ink is laid down on the plate and on the substrate, whatever that may be. The anilox, doctor blade, plate mounting tapes, and drying curing technology cannot be left out of the quality equation. The same applies to web control: the control of tension.
Even if a press has less than perfect dryers, applying ink thinly speeds drying and is a step in the right direction. Wet or insufficiently dried ink can cause many problems. With UV, remember that a certain amount of post curing with some substrates is possible. Blocking of stored rolls may be due to post curing issues. Ink that is still wet may lift from the substrate and, depending upon
the press set up, may transfer to the plate in the next deck. As the transferred ink builds up, the image produced will become progressively dirtier. Another problem with wet ink is poor trap. Trapping in defined as laying one colour over another to produce a third colour. If the first colour being laid down is not dried sufficiently, the second colour bleeds or mottles into the first. Thin ink film traps better due to its more uniform ink coverage. Large solids appear even and consistent as a result of applying ink thinly using an appropriate anilox and doctor blade. Type prints sharper because the controlled ink layer on the surface of the plate does not build up on the shoulders of the plate so easily. Reverse type benefits the
most. Less ink means that smaller point sizes can be reproduced without the danger of fill-in. This is particularly important if a converter is engaged in pharmaceutical applications, for example, an indistinct spot or blemish in the wrong place could compromise dosage instructions. A key advantage of flexo is the ability to work with a broad range of substrates, making it more able to respond to contemporary trends in design, packaging applications and to on-going changes in technology associated with the structure or format of the pack. The introduction of hybrid press units with integrated digital printing and complimentary inline converting capability strengthens a converter’s position in the marketplace, enabling
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February 2024
www.convertermag.com
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