Q&A: EB-Curing Technology
by Stephen C. Lapin, Ph.D., BroadBeam Applications Specialist
PCT Engineered Systems, division of ebeam Technologies, Comet Group
EB lamp (front/center), power supply and cooling unit.
Q. What types of applications are enabled by sealed tube EB lamp technology?
A. Low energy self-shielded electron beam (EB) systems have been used in industrial applications for more than 30 years. Early systems operated mostly in the 175 to 300 kV range and were designed for web processing up to about 3 meters wide. These systems were large and expensive but were a good fit for many applications, including crosslinking of polyethylene-based films for heat shrink packaging. This equipment also was being used for curing inks and coatings for package printing applications, but itwas really overdesigned for this use. A new generation of smaller EB systems operating from about 80 to 125 kV were introduced in the early 1990s. This lower voltage equipment was well-suited for curing thin ink and coating layers.
These first- and second-generation systems share some common features in that both use multifilament cathodes contained in a vacuum chamber. Electrons are accelerated through metallic window foils, which separate the vacuum chamber from the product being treated at atmospheric pressure. These foils are held in place with O-rings and mechanical clamps. The vacuum is maintained by continuously operated vacuum pumps. Periodic replacement of windows foils is part of the normal maintenance for these systems.
Another new type of EB system also was being pioneered by inventor Tovi Avnery in the late 1990s and early 2000s. This evolved into a startup company, Advanced Electron Beams (AEB). The AEB emitter was quite different from the early generation EB systems in that the new systems used a sealed window foil (not clamped) and maintained a permanent vacuum, eliminating the need for vacuum pumps. Rather than replacing window foils, new emitters were designed to “plug in” in the event of an emitter failure. Failed emitters were returned and rebuilt at the factory. This concept was more like a “lamp” than a traditional EB system.
The compact AEB emitters were available initially in 250 to 400 mm widths and were a small fraction of the size of the actively pumped systems. AEB produced a few hundred emitters and established some new applications, but eventually went out of business.
Following the demise of AEB, the development of optimized industrial sealed tube EB “lamps” was completed by the Comet Group. Design improvements were facilitated by Comets long history and experience in metal/ceramic industrial X-ray tubes. These lamps are currently available in 270 and 400 mm widths with accelerating potentials of 80 to 200 kV. Long lamp life (minimum of 6000 hours) has been proven even under severe cycling and use conditions. The development of reliable EB lamps has created opportunities for new EB applications.
EB Lab Systems: The large industrial EB systems are still widely used today. These systems are not well suited for product development in a laboratory environment due to the size, cost and utility requirements. The industrial systems also are designed mostly for high-speed web processing, whereas handling of individual sheets, panels or parts is often preferred for laboratory testing. Compact self-contained EB lab systems using EB lamps are now readily available to meet this need. The systems can handle A4 size sheets and parts up to 50 mm high. Dose and voltage can be adjusted to match beam conditions used in large-scale industrial EB equipment.
In-Line Package Sterilization: The use of EB to sterilize packaging is well known. High energy (1 to 10 MeV) EB is being used to sterilize full cases of packaged pharma and medical products. The high-energy equipment is very large, expensive, and requires conveyors within a shielded vault. These service facilities operate off-site from the product manufacturing and packaging. Compact EB lamps are ideal for sterilizing surfaces of packaging or of a product before it is packaged. Consequently, low energy (80-200 kV) lamps enable in-house and in-line sterilization of pharma and medical products and packaging.
Because the lamps are a good size to match individually packaged products, they integrate well into lines in which products are EB treated and maintained within a sterile zone for subsequent processing, packaging or sealing. Chemical-free EB sterilization offers an attractive alternative to sterilization with hydrogen peroxide, ethylene oxide or steam.
Narrow Web Printing: The use of traditional EB systems for wide web curing of inks and coatings for package printing applications is well known. The consistent beam output and photoinitiator-free formulations make EB attractive for use in food packaging applications. Narrow web printing is also an important process for the production of tags, labels, packets, tickets, lidding, etc. Historically, migration has been a lower concern for these markets; however, there is a growing concern about migration for labels and other narrow web-printed packaging.
Interest in digital printing is growing rapidly, driven by the demand for short runs of custom-printed packaging. Initial growth in digital package printing is occurring in narrow web formats. Rapid growth is expected for EB curing of inkjet inks and EB coatings on electrographic digital printed packaging. The fit of EB technology with digital printing will be the subject of future articles.
EB Curing on 3D Parts: EB has been used predominantly for curing of coatings, adhesives or parts conveyed through the EB units on a continuous web. Webs can be processed readily through EB systems using compact shielding and low volumes of gas for inerting.
Compact EB lamps offer the potential to change this paradigm. Lamps can be configured and used together with automated product handling to present all surfaces that require curing within the needed proximity of the beam window. Systems have been designed to maintain product shielding and inerting during this 3D curing process. Initial targets include curing inks (conventional and digital) on relatively simple objects including bottles, cans and tubs. EB curing on more complex parts, using multiple lamps systems, also is expected.
EB lamps certainly are a game-changing technology. Many new applications are expected that were not possible with traditional EB systems.