Deep Cure
Any fears of inks not being fully cured, however, are being overcome by new technology that delivers consistent output as a way of better ensuring full cure with migration issues under control. For the previously mentioned reasons, an inline press equipped with UV LED lamps for labels is not necessarily the right system for all types of flexible packaging at required profitable speeds that are sufficiently cured.
UV LED/EB inks with reduced special photoinitiators can be completely deep cured with a final electron beam unit. Between colors, UV LED lamps can partially cure, or tack, the ink, eliminating the wet on wet ink process. Final cure is with the E-Beam unit, thereby eliminating any fears of set off backside ink in printed rolls, through migration and food contamination. The cost of E-Beam units can be justified by the reduction in photoinitiators and operating costs.
Expanded Gamut & UCR
A standard 7-color ink set—CMYK, orange, green and violet—cuts pre-production lead times by removing the need to qualify new inks every time you go to press. You’re eliminating things like washup time on press and scrap with quicker setups, not to mention the savings in ink waste with multiple washups daily.
By using under color removal (UCR) color separations, you can save between 10 percent and 28 percent
in ink costs. Additionally, run speeds can be higher because the reduction in ink layers leads to faster curing.
Barrier coatings, currently under development, can be applied on either side on the last station of the flexographic press, or with a dedicated station, prior to the E-Beam unit for instant cure. Even though the UV LED/EB inks are fully cured, the barrier coating or overprint varnish (OPV) further mitigates any fears of ink migration. It is also possible to add a downstream station for special coatings in register to the main press on the front or back of the web.
Mike Sajdak, senior R&D chemist at INX International, adds the following: “At least in the US, a vast majority of customers printing food packaging-related items with UV flexographic inks, whether for flexible packaging or tag and label, will simply apply a UV coating. This is generally a gloss UV coating, as it is less expensive than laminations. Part of the draw to running UV LED flexographic inks is that the resistance properties are inherently higher and application of a UV coating is often adequate for many applications. Coatings can be gloss, matte, satin, textured, soft touch or any combination of those listed.”
By surface printing, instead of reverse printing and laminating, it is easier to separate color, odor and other contaminants from plastic waste to make virgin-like resin. Systems like PureCycle that use technology originally developed by Procter & Gamble Co are coming to market in rapid time.
“Today’s increasingly common belief is that a mid web stack press, in the range of 34-in. to 40-in. with a larger maximum repeat, will provide the capability for a wider range of stand-up pouches and flexible packaging than a 27-in. wide press.”
Laminations
Customers will laminate when higher resistance is required to provide added protection against chemical, water, oil, gas (petrol), thermal or UV sunlight exposure. Greater resistance for more demanding applications often requires lamination. Most printers would try to go the UV coating route for cost, rather than laminate, but you sometimes can’t achieve the exact same resistance properties with coatings.
However, with electron beam, it would be possible to laminate two materials using E-Beam adhesives. By using reverse printed UV LED/EB inks, partially cured, followed by an E-Beam adhesive, applied just before the electron beam, would produce a fully cured ink and adhesive that could be slit on press and shipped quickly, thereby reducing material waste generated by separate operations.
Another option is surface printing and then applying a coating inline, before the electron beam unit, which makes it easier to remove contaminants during the recycling process.
Additional advantages include:
- E-Beam lamination does not require nitrogen because the adhesive is trapped between two webs and therefore no oxygen is present
- You do need nitrogen with an EB coating
- Lower cost—with EB coatings, no photoinitiators are needed
- EB adhesive remains stable until cured, so there is negligible waste compared to water-based or solventless adhesives
- Solvent- or water-based adhesives require a dryer with longer web path that could produce more waste and web handling problems with higher energy costs
Circular Economy
We do not know where the “circular economy” in packaging is going for sure. “Bio-based” and “biodegradable,” “recycling” or “reuse.” With new developments every day, this concept will keep converters flexible to this changing environment.
By using biorenewably sourced resin content, ink will decompose over time when surface printed. There has also been growing interest in water-based UV curing technology in the last decade. You will be able to move in any direction according to the dictates of the new regulations and developments.
The battle is on to show which materials will best serve all aspects of food protection, preservation and cost, yet meet the demands of the circular economy. Monolayer materials with barrier coatings with functional additives are becoming part of the landscape for sustainable packaging because of the pressure to recycle and reuse plastics. Multilayer materials will certainly see some changes.
Plastic recycling faces many challenges, ranging from mixed plastics to hard-to-remove residues, to a cost-effective and efficient recycling of mixed plastics being perhaps the biggest challenge facing the recycling industry. Experts believe that designing plastic packaging with recycling in mind is the only way to meet this challenge.
Pressure will be on the converter to apply barrier coatings with functional additives inline and at the same time, reduce waste generated. All production waste, even at the converter’s plant, will also need to be recycled with all costs accounted for.
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