Edging out the Competition

Today’s package printers know that the more appealing a package looks to the consumer, the more they will reap monetary benefits. With this in mind, printers have been juggling the demands of high-productivity, easy maintenance, and environmental responsibility. It’s no wonder that because UV and EB technology allows for these benefits, it has been a major presence in the packaging industry. According to a RadTech International report titled, “Radiation Curing for Packaging,” the non-profit UV and EB organization expects that the currently estimated $480 million curing market for packaging will jump to $550 million by 2009.

With UV/EB technology increasing momentum, converters must know how to effectively use their systems to produce packages that hold up in a competitive market. packagePRINTING spoke to UV/EB suppliers, who shared tips on operating and maintaining the systems.

Finding the right cure

UV/EB curing uses an ultraviolet (UV) or electron beam (EB) light to polymerize monomers and oligomers onto a substrate, solidifying UV and EB materials into inks, coatings, or adhesives. When a UV lamp output is much higher or lower than what is needed, inks will not be accurately cured. “Overcured ink becomes brittle and cracks; undercured ink does not adhere and smears,” says Dave Douglas, vice president of business development for PRI Technologies. “If the ink is cured properly, it should pass an aggressive scratch test, a tape pull test, or an MEK rub test.”

Dan Cunningham, director of product development for Air Motion Systems, explains that an MEK (methyl isobutyl ketone) rub test involves using a cotton swab, weighted hammer with a cotton pad, or a “q-tip,” determining the number of “rubs” or strokes that it takes to “break” through the coating. He says abrasion tests may also help, in which an “abrasive pad attached to a weighted arm that is drawn or rotated at a consistent rate until the coating ‘breaks’ or fails. This result is denoted by the number of ‘rubs’ that are achieved.”

According to Brian Wenger, VP of GEW Inc., under-curing is seen when the ink or varnish is still tacky and full UV curing has not taken place. “Most press operators use an alcohol rub test whereby an alcohol soaked cotton swab is rubbed across the irradiated ink to determine if they are absorbed into the swab indicating under cure,” he says. “For varnishes, an aqueous solution of potassium permanganate is wiped across the varnish, which will oxidize any non-reacted varnish. An under-cured varnish will then darken depending on the degree of under-curing: the darker the test solution, the greater the under-curing.”

Cunningham suggests using a “pen test” with a permanent marker to check for accurate curing. “Properly cured coatings will make the ink from the pen reticulate or bead up on the coating,” he says. “Improperly cured coating will allow the marker ink to lay flat with little or no reticulation.”

The terms “over-cured” or “under-cured” refer to UV exposure that is outside of an acceptable process window, according Dick Stowe, director of technical communications, Fusion UV Systems, resulting in damaged, heat-sensitive substrates and a deficiency of cross linking.

“First and foremost the end user needs to understand the ‘cure window’ of the materials they are trying to cure,” says Ed McGhee, industrial sales manager, Nordson UV Systems. “They need to know the minimum and maximum energies they need for proper cure. They will need that ‘cure window’ in both millijoules and irradiance. This normally is supplied by the material supplier but, should always be verified by the end user.”

Wenger says, “It is important to accurately match the curing required with the UV lamp controls. Most UV systems have power ramping linked to the speed of the press. The level of power steps depends on the UV system specification and can be three, five, or more steps, or even infinitely variable.” UV chemistry requires a certain depth of cure, says David Samide, marketing manager, Prime UV Systems. “A perfectly designed elliptical reflector will achieve complete depth of cure at maximum process speeds,” he says. “A parabolic reflector system is fit for slower speeds and/or surface cure only.”

Wenger warns not to confuse a curing problem with an adhesion problem. “A number of circumstances can cause poor adhesion, particularly on filmic materials,” he says. “Ink compatibility with the substrate, lack of proper pre-treatment of film, and even over-curing can cause adhesion problems due to a brittle condition.”

Unlike UV curing, EB involves electrically heating tungsten filaments to generate a cloud of electrons that accelerate at high speeds through a foil window to penetrate the material. The electrons cause molecular changes in the product to strengthen polymers; cure inks, coatings, and adhesives; increase scratch, scuff, and abrasion resistance; increase chemical resistance; or create memory for shrink film, according to Energy Sciences Inc. “For EB systems, substrates being over- or under-cured isn’t an issue,” says Rick Sanders, marketing and sales executive, Energy Sciences Inc. “EB simply changes the applied chemistry (ink, coating, adhesive) from a liquid state to a solid state instantly without heat or light.” He recommends making sure that the EB dose and voltage settings are appropriate for the chemistry being processed.

Maintain open communication

In maintaining a UV/EB system, it is important to work closely with the supplier, since each operating system can vary from the next. For example, to make sure that UV systems are operating properly, PRI Technologies suggests inspecting bulbs every 800-1000 hours, according to Douglas. “A UV bulb will begin to turn black at each end and grow towards the center as the bulb ages. The areas where the black has started to appear will inhibit the bulb’s curing ability,” he says. “As for as the right bulb for the right application, the UV curing system manufacturer should be contacted to ensure the application is correct.”

GEW recommends UV lamps and reflectors be inspected and cleaned with a cotton cloth and isopropyl alcohol after running for 500 hours, and lamps be changed every 1,000 hours. And, Prime UV says regular maintenance can allow for longer run times. “UV bulb life can vary due to the cleanliness of the converting facility,” Samide says. “When proper preventive maintenance is performed, we have seen our customers run bulbs in excess of 3,500 hours. Prime UV suggests preventive maintenance be performed on the inner-lamp module and the UV system on a weekly basis, until the converter can set up a preventive maintenance schedule.” He also stresses that purchasing UV bulbs and system parts directly from the manufacturer for maximum lamp life and system performance. “Serious and sometimes unrepairable damage can occur when ‘second source’ bulbs and parts are installed that do not meet the UV OEM’s exact specifications,” he says.

Maintenance of the system’s cooling apparatus is key to making sure lamps do not overheat, says Cunningham. “Whether the housings are water cooled, which aids in lamp stability due to a cooler environment, or they are air cooled, the devices providing this cooling need to operate efficiently and consistently,” he explains.

According to Sanders, the filaments in EB systems need replacing every 10,000 production hours. Like UV curing, EB has maintenance guidelines that should be followed. “But generally speaking, EB systems don’t require ongoing cleaning,” he says.

Whichever system the converter uses, it is important to work with the supplier to help maintain the critical parts housed in each unique system, and to determine if they are using the right parts for a specific application. “Every UV curing system manufacturer has its own set of guidelines for operating and maintaining its system,” Douglas says. “As long as these are followed, problems and irregularities will be avoided.” pP

Resources

Air Motion Systems www.airmotionsystems.com
Energy Sciences Inc. www.ebeam.com
Fusion UV Systems www.fusionuv.com
GEW Inc. www.gewuv.com
Nordson Corp. www.nordson.com
PRI Technologies www.superblue.net
Prime UV Systems www.primeuv.com

UV Innovations

Versiflex UV Curing Systems

AAA Press’s Versiflex UV Curing Systems feature PLC-controlled electronics combined with rugged, flexible irradiators to deliver performance, mobility, and reliability. The LIGHTouch Versiflex Programmable Logic Controlled UV Curing System offers converters a proven performer for reliable everyday UV production. Versiflex UV systems include configurations with up to 14 lamps, automatic and manual five-stage intensity adjustment, and full programmability through the color touch-screen operator interface.

The systems feature a programmable full-color touch-screen remote for UV intensity auto ramp, shutter timing, and bulb timers; a micro adjustable UV intensity at five levels; on-screen trouble shooting and auto UV fault protection; dual filtered “cool” UV lamp assemblies in 400 or 600 W/in.; and a stepped ellipse reflector.—AAA Press International, www.aaapress.com

Deep cure UV technology

IST METZ GmbH has introduced a product range called Deep Cure Package (DCP), which has been designed specifically to cure inks that are difficult to process. This applies particularly to applications using opaque white, which require customized UV technology to guarantee a total cure of these inks, even at higher production speeds.

The two key elements of the DCP system are specially doped metal halogen lamps and cold-mirror UV reflectors, which are both customized to meet the needs of each specific application.—IST America, www.ist-uv.com

“Cool” UV curing

The UltraPak arc lamp offers the option of true “cool” UV curing of inks and coatings on heat-sensitive materials for almost all makes of narrow-web presses, including Gallus, Aquaflex, Webtron, Mark Andy, and Nilpeter. The UltraPak system uses an optional dichroic reflector and quartz IR filter in combination with superior heat-management features to permit efficient curing of inks or coatings without the use of chill rolls.

The UltraPak system uses a unique 0.75˝ (19 mm)-diameter bulb on its 400 W/in. (160 W/cm) mercury lamp system for a more focused exposure area and efficient cure.—Aetek UV Systems, www.americanultraviolet.com