Toward a Painless Cure

UV equipment developments are surfacing almost as quickly as new applications for the technology.

by Kate Tomlinson, Assistant Editor

THE SHRINK SLEEVE is just one of the latest packaging structures forcing suppliers to keep in step with the technology needed to process thin film substrates such as PET-G (the most common for shrink sleeves).

So what are bulb and UV curing equipment manufacturers doing to meet these rising demands? Bulb suppliers such as Primarc UV Technology are working to improve standard bulb life. Curing systems manufacturer Honle UV America has released its Advanced Cold Mirror (ACM) UV curing system, which reduces damaging heat by up to 70 percent. Prime UV Systems has recently installed UV dryers for shrink film lines running 1 mil film.

James McCusker, president of Honle, says curing UV inks and coatings on shrink film requires UV suppliers to be sensitive to the heat generated by conventional UV systems. "The ACM UV system maintains a high UV peak intensity to the web, allowing successful curing while running the press at full speed. It also eliminates conventional UV equipment using a chilled drum, which can be a costly solution," he says.

J.E. Doyle Co., known for its line of quality control systems, recently announced it has teamed with German supplier PrintConcept GmbH to distribute Print Concept's line of air- and water-cooled UV curing systems. J.E. Doyle President Joseph Lynch says these systems boast a compact lamphead design, a cassette system that provides uninterrupted production, and high-volume water cooling to reduce IR.

Don't shrink from sleeves

Hanovia's Jeff Andrews, director of sales and marketing, says while the company has not specifically designed systems for shrink sleeve applications, they have provided UV technology for similar supported and unsupported film stock requirements. "Typically dichroics, coated quartz filters, and cold mirrors are used on delicate film applications," he says, "all of which are designed to minimize the IR signature on very thin substrates."

Due to the variety of ink colors printed and the different spectrum of densities required when printing film applications, compatiblity of ink system and UV curing system on press is very important. "To get the perfect cure on shrink sleeves, the number one priority needs to be ensuring the ink, bulb, lamp, and power supply all match," says Mark Hahn, director of sales and marketing at AAA Press. He explains it is vital to keep the web cool during the cure process, which is best done with cool UV packages using dichroic filters and variable exhaust systems. "Another alternative to the standard three-step UV controller is a multi-step power supply with at least 20 steps between 150 wpi and 600 wpi for tighter control of curing power and better heat management."

"Customers are looking for highly efficient UV curing systems, allowing them to successfully cure UV inks with coatings at fully rated press speeds up to 800 fpm (in flexo presses)," McCusker says. "Because of the shrink sleeve stock's thermal sensitivity, customers are now demanding cold mirror technology for processing these films … UV curing solves more challenges."

Another way to keep the challenges to a minimum lies in monitoring the lamp's voltage, current, and power. Nicollet Technologies offers electronic ballast systems (EBS), such as its newly introduced version Gen 3, which powers the UV lamp. This system replaces conventional high-voltage capacitor banks and mercury-filled relays with an electronic control that provides continuously variable power. Jon Wilkie, president of Nicollet Technologies, says this type of equipment offers the ability to integrate the UV lamp controls into the process, allowing the printer more control for higher-quality end products.

"The ability to continuously vary lamp power from 30 percent to 100 percent allows the printer to optimize UV power to the chemistry of ink and substrate," says Wilkie. "Important issues typically associated with EBS systems are UV power required; spectral characteristics needed; chemistry of inks; characteristics of substrates; compatibility issues; production rates; lamp housings; lamp cooling considerations; the environment; and operational safety."

According to Eleanor Midlik, president of Prime UV Systems, both flexible packaging and folding carton converters run UV coatings on the majority of their packaging. In the last two years Prime UV has seen many beverage carton converters add UV capabilities to run UV coatings on the cartons. "The UV coating packaging market is the most vibrant, constantly growing segment of the industry," she says. "Whether printing gravure, flexo, or offset, the converter can add a UV curing station to their line to cure coatings over the printed product. High-end labels have used UV inks and coatings for years, and this technology has now spread to the mid-web and wide-web flexo printing market."

For printers curing inks or adhesives on the underside of the web (where UV light waves have to travel through the film), Midlik adds a more unusual troubleshooting tip is to make sure there are no UV inhibitors in the film. This is especially important in UV laminations.

Hahn advises checking a few quick basics before starting a job. "Most film materials are corona treated during the manufacturing process, but converters should typically bump treat them in-line on press to ensure the perfect printing surface … and for the ink to adhere, the film's dyne level must be at least 10 dynes higher than the ink's." He also suggests checking with the ink supplier to ensure they have included the proper chemistry for thick, dense colors, like black. "Printers often have trouble 'through-curing' dense colors. Make sure it contains photoinitiators targeting both short and long wave lengths for surface cure, depth of cure, and bond to the substrate," Hahn states.

Seeing the light

Today, different methods are used to excite the metals and gases within UV lamp bulbs. There has been a drive to increase the energy output of UV bulbs, which introduces its own set of challenges, including UV energy focus and bulb cooling. "It used to be common to have a lamp with an output of 200 wpi," says Jeff Bade, sales manager at Primarc UV Technology. "Today, 400 wpi and 600 wpi systems are more common, with at least one dryer manufacturer designing systems to have an output of over 1,000 wpi," he says.

Generally, a bulb's arc length should be 2˝ longer than the width of the substrate. This allows the printer to ensure sufficient curing along the substrate's edges over the useful life of the bulb. "It's more important, however, that the printer develop a strong relationship with their material suppliers," says Bade. "Ink and coating chemistry must be matched to the UV energy available to the printer. A failure to do so will affect ink/coating cure rates, which reduces throughput, thus affecting the printer's ability to compete."