FREEcure: A new era of UVC curing for Roll-to-Roll converters

Abstract

The roll-to-roll converting industry is under constant pressure to balance productivity, energy efficiency, and regulatory compliance. UV curing has long been a proven method for instant crosslinking of coatings and inks, yet traditional systems rely heavily on photoinitiators and inertization. FREEcure, developed by IST METZ GmbH & Co. KG in collaboration with BASF SE, represents a paradigm shift by enabling direct UVC-induced polymerization with drastically reduced or even eliminated photoinitiator content. This article examines the scientific principles, technological innovations, and industrial benefits of the FREEcure system, demonstrating its potential to redefine sustainable roll-to-roll curing.

The Challenge: Photoinitiators and Oxygen Inhibition

Conventional UV curing systems depend on photoinitiators to absorb UV light and generate radicals that trigger polymerization by converting carbon-carbon double bonds (C=C). However, oxygen inhibition at the coating surface limits reaction efficiency, causing slower line speeds and incomplete curing. Traditional countermeasures include inertization with nitrogen or excessive photoinitiator loading—both costly and environmentally problematic. Regulatory restrictions and supply constraints, particularly under REACH and more and more restrictions on Specific Migration Levels e. G. German Ink Ordinance and Swiss Ordinance, have further challenged the ink and coating industries to find photoinitiator-free alternatives.

The Physics Behind FREEcure

The development team at IST METZ investigated whether UV polymerization could be achieved through direct bond cleavage, bypassing photoinitiators entirely. Theoretical calculations indicated that photon energies exceeding 6.15 eV—corresponding to wavelengths near 202 nm—are sufficient to crack the C=C double bond directly. Hence, the objective became clear: develop a UV source capable of producing intense radiation around 200 nm without requiring an inert atmosphere.

Excimer and LED sources were evaluated but ruled out due to low penetration depth, ozone formation, and insufficient optical power. The medium-pressure mercury lamp, however, offered a broadband UV spectrum starting near 200 nm and could be modified for higher UVC emission. IST METZ engineers therefore based the FREEcure development on their proven BLK platform, shifting the spectral output toward the short-wave UVC range and increasing emission below 220 nm heavily.

This was achieved through optimization of plasma technology, improved reflector materials, specialized lamp materials, and refined electronic control systems. The resulting UV system exhibits extraordinary photon density in the UVC region, ideal for direct double-bond cleavage.

From Physics to Process: The Chemistry of Direct Curing

BASF SE contributed its expertise in binder chemistry to evaluate for UVC reactivity. Binder selection, functionality of binder, and amine modification proved critical for suppressing oxygen inhibition and achieving high conversion rates. In laboratory FTIR analysis conversion levels above 80–90 % were achieved without photoinitiators. Both 100 % UV and water-based UV dispersions were successfully cured.

The cooperation project thus bridged lamp engineering and chemical formulation, demonstrating that targeted synchronization between raw material and light source can yield process-ready systems. In many cases, FREEcure coatings displayed chemical resistance, scratch hardness, and gloss levels similar or better to conventional systems employing standard photoinitiator concentrations.

Implementation for Roll-to-Roll Production

In continuous web coating and printing lines, energy efficiency and footprint are decisive. FREEcure enables curing speeds up to 250 m/lamp/min for offset and flexographic printing, and 30–50 m/lamp/min in high-speed roller applications for furnitures or rear panels of cupboards. Depending on the formulation, as few as two to three FREEcure units may suffice, often supplemented by LED-UV for thick-layer polymerization.

Beyond eliminating photoinitiators, FREEcure offers significant economic advantages: up to 75 % lower energy consumption, CO₂ savings in the hundreds of tons annually, and amortization times between 1.5 and 2.5  years. The reduced number of UV units minimizes spare-part demand and line complexity, supporting compact and modular roll-to-roll designs.

Operator Perspective: 'It Cures Like Hell!'

Early trials with industrial users quickly confirmed the system’s power and reliability. During initial curing experiments, one operator famously remarked, “It cures like hell!”—a fitting description for a technology delivering radical performance without radicals from photoinitiators. Despite its humor, the phrase captures the excitement around FREEcure’s rapid surface polymerization and immediate handling strength.

Energy, Sustainability and Market Implications

The introduction of FREEcure aligns with global trends toward decarbonization and safer chemistry. Reduced photoinitiator migration supports food packaging and sensitive substrates, while lower energy input contributes to operational sustainability. Installation and infrastructure are additionally simplified by the elimination of inertisation requirements.

As environmental regulations tighten and consumer demand for low-odor, low-migration products rises, FREEcure positions roll-to-roll converters for future compliance and competitive advantage. Its modular integration allows retrofitting of existing BLK-based UV systems, providing a cost-effective upgrade path.

Conclusion

FREEcure marks a milestone in UV curing, merging advanced lamp physics with tailored binder chemistry. Its intensified UVC spectrum enables direct cross-linking of coatings without inertization or heavy photoinitiator reliance. For roll-to-roll converters, it delivers sustainability, speed, and uncompromised performance—truly redefining what’s possible in UV curing technology.

In summary, FREEcure combines energy efficiency, environmental responsibility, and scientific precision. With up to 75 % energy savings and full compatibility for high-speed roll-to-roll production, it paves the way toward photoinitiator-free, low-migration coatings. The future of UV curing has never looked brighter—or cured faster.

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