- July 01, 1996, Mykytiuk, Andrew
Converters have been fueling the growth of the ultraviolet-curing industry at a rate of 20% per year for the past ten years. George Pasternack, manager of patents for DMS Desotech, Elgin, IL, says the original impetus behind the development of this technology in the early 70s was to eliminate the use of solvents, but users quickly discovered the technology also provided certain benefits that enhanced production, line speed, and performance.
"In any kind of printing processing, the slowest link has always been the drying stage. That's an area people look at to shorten the process," says Steven Siegal, president of UV Process Supply, Chicago, IL. Unlike conventional inks, adhesives, or coatings, their UV counterparts do not dry but are hardened through a curing process that occurs when exposed to light in the UV band. Photoinitiators within the formulation absorb UV energy, beginning a chemical reaction that quickly bonds everything into a tightly crosslinked solid.
In the early years of UV development, power was low - approximately 100 w/in. Since then a great deal of progress has been made. Lamp power has been increased to 400-600 w/in. with a commensurate increase in line speeds, and a variety of efficient reflector designs have been perfected. Today's bulbs contain precise custom mixtures of different metals to provide light at specific wavelengths to match the coating to be cured. This is important, because UV coating and adhesive chemistry has been greatly improved as well and now offers formulations that crosslink at specific parts of the UV band (200400 nanometers).
In recent years a new kind of bulb has debuted. Using microwave energy to deliver power to the bulb eliminates electrodes, which are the main cause of bulb failure. These bulbs come in 10-in. lengths and are suited to modular setups. David Blake, VP of sales/marketing for Fusion UV Curing Systems, Gaithersburg, MD, explains that these lamps can be stacked end to end to cover any width.
Electron beam technology, unlike UV, does not need photoinitiators. It delivers electrons at high energy directly into the coating. The amount of energy is high enough to break up the monomer and ligamer materials in the coating and rearrange them into a crosslinked form. An advantage of EB is that it works rapidly and, because of its inherently higher energy, can penetrate deeper into thicker coatings or coatings packed with pigment that are opaque to UV.
"We are on our fifth generation of equipment, and there has been steady evolution of electronics," says John Chrusciel, senior engineer for ESI, Wilmington, MA. "We have advanced the power output capability by almost four times since we started and can easily meet the speed requirements of the highest-speed presses and converting lines."
According to Chrusciel, there are some processes you can only do with EB, or gain maximum benefit from, such as the crosslinking of film for higher performance. Other advantages of EB technology are said to be consistency, degree of cure, low odor, and low downtime. Unfortunately, EB is quite a bit more expensive than UV, but ESI is on the verge of releasing a mid-web version claimed to cut the cost of EB technology in half.
As far as the future of these technologies is concerned, the trend toward higher power continues. Already common are lamps featuring 600 w/in., but even higher powered lamps will be available in the next few years because of customer demand. This new generation of bulbs will be tuned to emit light at a narrow frequency, while emitting drastically reduced amounts of visible light and undesirable heat in the form of IR energy.
The electronics revolution has affected UV/EB technology in a big way. UV Process Supply offers a variable power supply that allows the adjustment of lamp output from 25% to 100% of the rated value. And new lamp-monitoring devices measure the lamp's degradation for added process consistency. The fight to continually improve productivity is providing the impetus for manufacturers to constantly improve and upgrade their technology.