Viewpoint: Terry Thompson

As converters seek ways to break through to new levels of product excellence, they have begun to realise that not all converting processes are created equal. Looking beyond traditional thermal drying techniques, forward-thinking converters, especially those using web technologies, are turning to solvent-free curing solutions such as ultraviolet light (UV) and electron beam (EB) technology.

EB technology continues to grow in popularity as a curing and cross-linking solution, as converters continue to realise its advantages: improved product performance, superior product consistency, higher process throughput, greater energy savings, and that it is a 'food safe' technology.

EB begins with a cloud of electrons being generated inside a vacuum chamber using an electrically operated filament. Theseelectrons are then accelerated through a thin, metallic foil window onto a moving web surface at atmospheric pressure. These accelerated electrons can ionize most organic materials, which form free radicals. This free radical either: (i) cross-links polymer materials; (ii) initiates the polymerisation of liquid monomers and oligomers (curing); or (iii) does both. Cross-linking can be an effective way to improve the properties of polymers; while curing produces an instantaneous 'drying' of inks, coatings or adhesives.

EB systems are most often associated with curing printing inks and coatings for packaging applications. Additional applications that have built momentum in recent years include curing adhesives for the lamination of films, foils and paper for packaging; cross-linking plastics shrink films; and cross-linking of hotmelt pressure sensitive adhesives.

From a performance perspective, EB provides higher conversion and more consistent output; and offers more efficient energy usage than other drying or curing technologies. It is able to penetrate opaque materials more effectively than UV. EB machines also generate very little heat in the substrate, making them a superior choice over thermal and UV curing for heat-sensitive materials like thin films.

Because the process is capable of both curing and cross-linking a substrate, package exteriors can attain an added level of durability above other curing processes.

EB technology offers sustainability advantages over thermal drying, which include low energy usage and the elimination of emissions of volatile organic compound (VOCs). EB curing is also considered to be more attractive for food packaging than UV curing, as it offers high conversion, constant output, and the elimination of photoinitiators which have a potential for migration.

Another advantage applies to the actual mechanics of incorporating EB systems into web processing lines. Material to be processed is safely transported into a shielding structure and is uniformly presented to the electron beam, which is emitted through the window foil. Maintaining a controlled distance and inert atmosphere between the product and the EB window is important to ensure consistent curing. Recent innovations that help do this include:

¦ Integrated Shield Roll Design: This patented design uses a temperature controlled roll that supports the material during curing and simultaneously shields any generated radiation. This reduces the size of the machine, provides additional web path tension to move material into and through the curing area, minimises the area that requires nitrogen inerting, and offers easier machine access for threading and cleaning.

¦ Low Profile: Recent EB system designs can also accommodate web handling requirements by providing a 'side fire' beam orientation. This makes the machine much more accessible when maintenance is required to change window foils. In addition, an important printing technology that has emerged in recent years involves the use of variable sleeves on web offset presses, which require an accompanying EB system to accept a low web entry height.

¦ Extended Voltage Low Energy Systems: The first generation of more compact, lower cost EB equipment introduced about 13 years ago operated at a range of 80-125kV for curing relatively thin layers of inks and coatings. In recent years, more powerful compact equipment has been introduced that can operate at up to 175kV. This allows curing of thicker coatings and adhesives for laminates or cross-linking of thicker materials without the need for larger, high cost systems that operate up to 300kV.

EB is continuing to gain prominence. Forward thinking coating, ink, and adhesive manufacturers continue to develop an expanding variety of EB curable materials, adding to its attractiveness among converters. Also, EB systems themselves continue to grow more affordable.

As the size, cost and complexity of EB systems continue to grow smaller, narrow web printing and converting has become an ideal arena in which to expand EB technology. A new generation of compact systems utilising sealed emitters has helped drive down costs and slim machine sizes. Armed with EB curing solutions, narrow web printers are now looking to expand beyond labels into food packaging.

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