Editor’s Note: Part 1, which appeared in Quarter 3 UV+EB Technology, discussed how EB and UV were practical and sustainable solutions for the coil coating industry. Part 2, which appeared in Quarter 4 UV+EB Technology, hosted a discussion on 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 continues with the challenges in incorporating EB and UV into the coil coating process.
Challenges
Practical, sustainable, economical, safety, enabling – all different lenses through which implementation of EB and UV can provide solutions to the coil coating industry. Technology with a myriad of solutions? What’s the catch?
Weathering data
Several challenges exist in incorporating EB and UV into the coil coating process; chief among them likely is the relative newness of the technology in coil up against the 30- and 40-year warranties of pre-coated coil’s largest application – construction. EB and UV are established technologies, and all of the pieces of the puzzle required for coil coating already exist in commercial production – weatherability, durability, flexibility, gloss level, adhesion to metal. Until very recently, these pieces were scattered across all different industries from exterior décor panels to flexible food packaging to metal pipes. And the combination of these properties, while possible, is not trivial to achieve, especially within the constraints of the coil coating process.
The involvement of EB/UV in coil coating was foretold a couple of decades ago. 1 Paint companies invested in developing solutions, but the industry was not ready, and the research was, in large part, paused. Within the last five years, engagement from some influential companies reignited interest and resulted in commercialized products. The problem? Even with this history, the real-time weathering data is limited. As Pauline Maillot, Americas Technical Director for Beckers Group, puts it, “The first generation of EB and UV panels in the field are not the coatings of today. Today’s coatings, using newly developed materials, have not been on the fence for very long.”
Paint companies are stepping up development in anticipation of more coil coaters incorporating EB and UV in the near future. They are utilizing a combination of real-time weathering and accelerated weathering data to predict the longevity of the current generation of paints, but it is challenging to match predictions against conventional panels that have sat on a fence in Florida for more than
50 years.
Lack of solvent
Another coating challenge stems from a lack of solvent. Solvent may be poor for the environment and human health, but it is excellent for viscosity control. Without solvent, EB and UV systems use reactive diluents – monomers – to reduce viscosity, but because these diluents become part of the cured paint, they also have an influence on the paint’s properties. Every viscosity adjustment could require additional property evaluation. Furthermore, better performance and increased flexibility generally come from higher-molecular-weight oligomers, which are more viscous than their lower-molecular-weight counterparts. If a paint is too viscous, it cannot wet-out properly at high line speeds and adhesion could suffer. This delicate balance of viscosity and performance can be difficult for formulators, but as experience is gained and new monomers and oligomers are developed with coil coating in mind, formulating should become less arduous. In addition, temperature control of the paint can support formulation in reducing viscosity.
Solvent also aids in gloss control in conventional paints. As the solvent evaporates, matting agents are left protruding from the surface of the coating, scattering light and producing a matte effect. Matte coatings are achievable with UV and EB systems, but without an evaporative fraction it is harder to force matting agents to the surface. Alternatives that have been used in other industries are gallium UV lights and excimer. The long UV wavelengths (spectral peak ~405 nm) produced by gallium bulbs penetrate more deeply than those of standard mercury-arc bulbs, causing a slower rate of cure at the surface compared to the depth, which, in turn, encourages matting agents to migrate to the surface (or phase separation to occur), and gloss reduction is attained. Excimer works in an opposite manner to accomplish the same effect; short wavelengths of light (172 nm) only cure a very thin layer at the surface, which results in micro-wrinkling that scatters light and reduces the gloss level.
Equipment
Additionally, coil provides some challenges from an equipment perspective. In other applications, roll-to-roll materials tend to be flexible webs of paper, plastic or even thin metal foil. Rigid materials tend to be sheet-fed. Metal coil bridges the gap, being both a continuous web and semi-rigid. These qualities require some new design considerations from EB and UV manufacturers. The air gap – the distance between the beam or lamp and the product – often is kept quite short to minimize energy loss and nitrogen usage, but these also are some of the most delicate areas of the equipment. Allowances need to be made for protruding stitches between coils or possible damage due to loss of strip tension. Rollers incorporated into EB or UV systems need to withstand much higher tensions than seen in paper or plastic applications and be of sufficient diameter to avoid coil set in the metal. Solutions for these new design challenges already are being implemented on some coil lines, and they likely will continue to evolve.
Transitioning
Transitioning technologies from conventional thermal coatings to EB- and UV-curable versions is a challenge in itself. Like other industries before it, coil coating is entrenched in the status quo of heat and solvent – the infrastructure, the investment, the experienced workforce. For decades, this combination has produced a robust product portfolio that has performed remarkably well against the wrath of Mother Nature and the march of Father Time. When challenges arise, they are measured, and operators know how to respond.
So, don’t throw the baby out with the bathwater. A company can start small – for example, raising the value of an existing product by adding a rad-cure coating. This article is aspirational in many ways; it paints a vision of a solvent-free, oven-free future and the benefits that follow, but that future doesn’t have to be tomorrow or next week. There is no set pace, except, perhaps, to contribute to the carbon-neutrality goals of 2050, and almost any step toward a greener future is better than standing still. On the other hand, do not confuse a lack of a specific timeline with a reason not to start transitioning. EB and UV are not difficult technologies to learn, but there is an adjustment period to navigate.
Integration into existing line
Beyond the initial development work that can take place using panels and a small lab set-up, there are two paths forward: (1) adding EB and UV onto an existing (or new) conventional coil coating line or (2) building a new, separate line for EB/UV. In the case of the first option, the initial investment is likely smaller, but limited space may influence which technology or technologies are included, and, assuming it is a production line, the production schedule will dictate when and for how long experimentation may occur. Line speed will be tied to upstream processes. Once a qualified product is developed, however, the entire process can take place in-line.
Building a new line
The second option is a larger capital investment, but it also provides a flexibility that the former cannot match. Space likely is less of a constraint (along with line speed), allowing for the possibility of different printing, coating and/or special effects technologies in addition to EB/UV. Experimentation and training will not interfere with existing production. And some of the advantages of the technology, such as the ability to stop and start with little to no waste, will be more readily apparent. It is assumed in the first case that a mix of conventional and EB/UV technologies will be used, but in this second case, a full EB/UV coil coating line from backing to primer to top coat is not a necessity either. It will mean scheduling production time to create coils with whatever layers are to be conventional, but it is a possibility. With the proper forethought, space can be left for future components, and/or coils can be run through the line again to experiment with multiple EB or EB and UV layers as progress is made toward a completely solvent-free product.
Supporting the transition
Because of the robustness required, a coil coating line is not an inexpensive venture, no matter the size, which makes having a pilot line reserved only for trials difficult to justify. Instead, decide on a product. Does the lack of long-term weathering data create uncertainty? Perhaps this is an opportunity to branch into a new application. Not every piece of pre-coated metal needs a 40-year warranty. Pick and choose where transitioning makes sense and reduces risk. Know that initially the line may not be profitable, but over time (say, one to three years), the purpose of the line can shift from a pilot line that dabbles in production to a production line that still can be used for testing and trials.
Collaborate with paint providers. In this transition, they need the support of the coil industry, and the industry most certainly needs their support and guidance as they navigate new technology. EB, UV, UV LED, excimer – these technologies, while similar, are not interchangeable. Coating companies understand the nuances, and they can make recommendations. Or, at the very least, they need to know what technology they are formulating for. Similarly, they need to be aware of other coating layers on the coil to ensure compatibility.
A transition of this magnitude does not happen with the flip of a switch. It should not happen with the flip of a switch. There is a learning curve that takes time to master. The operation of EB and UV systems is not particularly complicated; however, the indicators of machine performance are different. Instead of temperature checks, operators need to learn how and when to do dosimetry. Instead of monitoring oven air flows, operators need to learn what it means if the vacuum spikes on the beam. Maintenance also is different. There are no burners to clean or flame sensors to check, but there are bulbs and filaments to change.
Start now, start with a purpose, and take the time to properly hone your EB/UV skill set. Develop an experienced workforce. Uncover and overcome challenges while the risk is low. Discover the advantages of EB and UV for your company. Scale when you’re ready.
Conclusions
In summary, EB and UV are multifaceted solutions that can propel coil coating toward a bright future. Be it for financial or sustainable reasons, whatever the vantage point, the same common themes hold true – EB and UV are fast, low-temperature and solvent-free – and will have reverberating effects on the industry. There always is a risk associated with making changes, but then again, what is the risk of not being ready for change?
Acknowledgements
Thank you to David Cocuzzi (NCCA), Marc Minon (RADSYS) and Pauline Maillot (Beckers Group) for their insights and contributions.
Reference
- Berejka, A. J., Electron Beam Curing of Coil Coatings, RadTech Report, Sept./Oct. 2003, pp. 47-53.
Resource
1. For a listing of some of the commercial products using UV/EB in coil, visit https://uvebtech.com/articles/2024/cleveland-steel-container-a-pioneer-in-uv-eb-coil-coating/.
Sage Schissel, Ph.D.
Applications Specialist
PCT Ebeam and Integration LLC
sage.schissel@pctebi.com
