EB and UV for Coil Coating, Part 1

For over 60 years, steel and aluminum coil have been coated with solvent-based paints and primers, dried in thermal ovens and transformed into metal siding, roofing, appliances, office furniture and more. In that time, advances in the technology have translated into better coating consistency, shorter bake times and faster line speeds, all while maintaining the necessary performance characteristics to offer 30- and 40-year warranties for many exterior applications. Among these changes, what has endured for the vast majority of coil coaters is the combination of solvent-based coatings and a heat source. This combination is ingrained in the industry from the supply chain to the infrastructure to the experienced operators. So it is not a trivial matter to suggest eliminating these foundational pillars and replacing them with radiation-curable chemistries and an electron beam (EB) and/or UV lights. And yet, now may be the time to start transitioning as EB and UV technologies offer solutions to present and anticipated future problems facing the coil coating industry.

A Practical Solution

Recruiting for manufacturing jobs is becoming increasingly more difficult. ¹ Stricter environmental regulations, pressure from consumers and the upcoming EU imports carbon tax have all impelled greener products. Evolving regulations may also limit the presence of some widely used chemicals, such as PVDF (polyvinylidene difluoride). PVDF is the product of PFAS pre-cursors (per- and polyfluoroalkyl substances); PFAS are also known as forever chemicals for their persistence in the environment and human body and currently are the focus of multiple regulatory agencies. Moreover, the recent pandemic and the ongoing conflicts have been a harsh reminder of the importance of supply chain diversity. The incorporation of EB/UV technology can help alleviate these concerns.

EB lines generally require fewer operators. The energy output of the beam is consistent; the filaments that generate the electrons either work or they don’t (and if the latter, the change is reflected on the operator display), there is no degradation over time and standard uniformity is achieved across the beam width. ² There is no adjustment needed for ambient temperature fluctuations. In comparison, oven temperatures may need to be raised in the cold of winter or lowered in the heat of summer to achieve a constant peak metal temperature (PMT). Over approximately 150-200 ft of oven length, different temperature zones may need to be adjusted independently to prevent cold or hot spots. This massive size also impacts maintenance requirements and access. In contrast, beams have a relatively small footprint (~10-15 ft) in line. What’s more, the ease of stopping and starting with little to no strip waste and almost immediate readiness provides flexibility in scheduling shifts, maintenance and holidays for operators. Production needs can dictate when the line is run instead of weighing them against the time and expense of reheating a cold oven and the strip waste incurred.

Both EB and UV are considered green technologies – energy efficient and not requiring solvents. EB- and UV-curable inks, paints, coatings and adhesives can be formulated to be PFAS free. Additionally, while most pre-polymeric and polymeric materials are derived from petroleum, the reactive materials in EB/UV formulations, namely acrylates, are not the same as the materials used in solvent-based thermal formulations. ³ The absence of solvent and the diversity in paint and primer materials do create opportunities for varied supply chains. Likewise, incorporating EB and UV technologies, which run on electricity, provides an alternative to the natural gas dependence of many ovens.

Having an alternative solution, like EB, that offers a clear path around these seemingly impending (or at least, possible) obstacles may go a long way in avoiding disruption to production.

A Sustainable Solution

Sustainability is an established concept in the coil coating industry. Steel and aluminum are infinitely recyclable – forging a foundation for a circular economy that plastic producers and consumers can only dream of. Pre-painted coil avoids the waste associated with over-spray and the variable coating thickness of post-painted metal (e.g., cars). ⁴ Furthermore, a significant fraction of pre-painted coil is used to manufacture products with decades of longevity.

And yet, there is room for growth. Coil coating lines are energy intensive. Ovens can span ~100 to 200 ft and typically operate at temperatures of 400 to 800˚ F (200-425˚ C) to achieve the PMT and dwell time. ⁵ Quench water (and/or air) is needed to cool the strip. The conventional paints contain a sizable amount of solvent (40-60%), which creates environmentally harmful volatile organic compounds (VOCs) that must be captured by oxidizers. In contrast, solvent-free EB and UV paints do not need to be heated to cure. No quench or oxidizer is required. These technologies support a relatively small footprint. What’s more, because there is no evaporative fraction, even less direct contributions to the carbon footprint, such as transportation and storage, are reduced.

RADSYS has constructed an estimating sheet to compare, in broad strokes, conventional coil coating to EB and UV. ⁶ Parameters for the strip, coating/paint and technology, found in Tables 1, 2 and 3, respectively, were chosen and input into the estimating sheet. Figure 1 demonstrates the predicted difference in energy consumption between technologies based on the chosen parameters. The conventional process, utilizing thermal ovens, has energy contributions from both natural gas and electricity. The natural gas contributions include the ovens and oxidizers, and the electrical contributions estimated are exhaust fan motors and water quench sprayers. No recovered energy from the oxidizers was assumed in this estimate and neither were the energy requirements to treat the quench water. The energy consumption of EB and UV is all electric.

A reduction in energy consumption can be achieved by switching from thermal drying to EB or a combination of EB and UV (see Figure 1). A fully EB line consumes the least amount of energy at just 290 kWh or 2.5% of the thermal line. The most energy intensive option of the rad-cure technologies is the combination of EB and UV (assuming UV for the backer and primer and EB for the top coat) with UV gloss control, and it is estimated at a mere ~6% of the thermal line. These percentages shift slightly with changes in speed but are fairly consistent over a broad range – the latter is predicted to remain at <10% of the thermal line from 80 to 600 ft/min (25 to 180 m/min). If IR or induction ovens are considered instead of natural gas, the energy consumption of the thermal process is decreased by ~20 and 43%, respectively; however, even compared against the least energy-intensive of the oven choices, the EB/UV + gloss control option requires just 11% of the energy of an induction oven. And, because the energy requirements for EB/UV are electric, the energy could be sustainably sourced.

Those familiar with the industry may point out that the coil coating process is not the most energy-intensive step of pre-painted coil. Indeed, Beckers Group estimates that the combined carbon footprint of the conventional coil coating process and paint production is approximately 1/10th that of the standard steel hot rolling process (see Figure 2). However, steel companies have made significant strides in recent years to decarbonize the coil-making process, and several have set goals to be carbon neutral by 2050.^7-9 When compared to a reduced carbon footprint steel substrate, the carbon footprint ratio of conventional coil coating + paint production to hot-rolled steel shifts to 1:4. As companies make efforts to decarbonize the steel-making process, adoption of reduced carbon footprint paint (e.g., EB- and/or UV-curable paints) becomes increasingly important to lower the overall footprint of pre-painted steel products.

Part 2 will discuss the value of savings related to the reduction in energy consumption and other factors, as well as the reduction in safety hazards for the coil coating industry. Part 3 will continue with the challenges in incorporating EB and UV into the coil coating process.

References:

1. Rudge, S. Persistent Labor Shortages are Endangering US Manufacturing Output. Manufacturing Today. Jan. 2025. https://manufacturing-today.com/news/persistent-labor-shortages-are-endangering-us-manufacturing-output/
2. Schissel, S. A Long-lived EB: Machine Function and Maintenance Part 1. UV+EB Tech. (1) 2022.
3. Arceneaux, J., Printers’ Guide: UV&EB Chemistry and Technology. 2016. https://radtech.org/archive/images/printers-guide-new/ChemistryPrimer_2016update_PROOF.pdf
4. Coil Coated Metal: The Green Alternative. 2021. https://uploads.prod01.oregon.platform-os.com/instances/1799/assets/documents/pdfs/Coil-Coated-Metal-The-Green-Alternative.pdf?updated=1627587504
5. Hall, D., Bonner, M.R., Monitoring & Control Technologies Produce Huge Savings for Coil Coaters. Coil World 19(1) 2014.
6. RADSYS spreadsheet. Contact Marc Minon at info@radsys.eu for more information.
7. Steel Dynamics Sets Goal to Be Carbon Neutral by 2050. Build Steel. https://buildsteel.org/why-steel/sustainability/steel-dynamics-carbon-neutral-2050/
8. Nucor Sets Net-zero Science-based Greenhouse Gas Targets for 2050. Nucor. Nov. 2023. https://nucor.com/news-release/nucor-sets-net-zero-science-based-greenhouse-gas-targets-for-2050-122870
9. Road Map to 2050. United States Steel. https://www.ussteel.com/roadmap-to-2050

Sage Schissel, Ph.D.
Applications Specialist
PCT Ebeam and Integration LLC
sage.schissel@pctebi.com