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A Hot-Melt Trilogy – Part I: Melt-on-Demand Systems

Posted on 1/21/2015 3:44:29 PM By Hallie Forcinio
  

Many packages would never arrive intact at their destination if it weren’t for hot-melt sealing. As a result, hot-melt systems are a common sight on packaging lines, the technology is constantly evolving, and interest is growing in melt-on-demand (MOD) systems.

Designs vary, but the most recent introductions are described as tank-free, or tank-less. However, “other design architectures…also provide on-demand melting, such as heated platens on drum unloaders, piston-driven slug melters and hot-melt extruders to name just a few,” explains Judy Bryan, global marketing communications manager at Nordson.

ITW Dynatec, which recently established a division to serve packaging applications, introduced its patented MOD technology in 1968. It consists of a vertical hopper with a heater core at the bottom. “There was an obvious need from customers at this time to reduce the amount of char and degradation in their adhesive systems in order to improve performance,” recalls Scott Hudanish, U.S. sales manager, Packaging at ITW Dynatec. “This technology has progressed over the years to include further innovations such as staged heating, cast-in heaters and improved hopper coatings,” he reports.    

All MOD hot-melt systems, including tank-less systems, “have some form of reservoir or holding capacity,” explains Hudanish. But regardless of the design, the goal remains the same – to heat the adhesive as needed and thereby minimize or prevent charring and degradation. Less char reduces or eliminates particulate matter, which can clog hoses and applicators and cause inconsistent adhesive flow, defective seals and downtime.

Increased productivity ranks as the primary reason for converting to MOD systems. Not only is there little chance of charring or degradation, but makeready time from cold start to dispensing shrinks by at least one-third from the typical 30 to 45 minutes needed with conventional hot-melt systems.

Melting adhesive as needed also conserves consumables. Percentages vary, but “it’s not unusual to reduce adhesive consumption by more than 15 percent,” says John Ferguson, strategic sales manager-Packaging at Graco. The reason is more consistent viscosity. “There’s a much smaller volume of glue you’re trying to keep at a particular temperature,” he explains. If you can keep viscosity consistent, you don’t have to oversize the nozzle,” he adds.

Finally, MOD systems consume less energy, about 20-25 percent less than conventional hot-melt systems and represent a lower burn hazard to operators.

In sum, Bryan says the benefits of on-demand systems are “mostly financial and come as a result of improved productivity, parent machine efficiency, and reduced maintenance and operator interaction stemming from virtually char-free operation, improved workplace safety, automatic adhesive filling, optimized adhesive usage, easy integration with parent machine and intuitive controls and diagnostics.”

MOD requirements

Advances in adhesives and automatic feeding technology have made the development of tank-less systems possible. However, it should be noted, not all types and forms of hot melt are currently compatible with tank-less systems, which require pelletized, vacuum-feedable adhesives. At the moment, this precludes usage of polyurethanes and pressure-sensitive formulas. In fact some tank-free systems may specify use of “certified” adhesives that have been proven to perform optimally with the system.

Tank-free systems also may require additional floor space to accommodate an auto-feed filler. Capital investment may be higher too, due to the cost of the auto feeder as well as more complex integration with the parent machine.

As with all packaging line equipment, output for a MOD hot-melt system should be matched to anticipated production volume.  

graco, tankless packaging, invisi pac, packaging

Tank-less MOD hot-melt systems like Graco’s InvisiPac models rely on automatic feeding of pelletized adhesive. 



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