A breakthrough assembly technology opens the use of thermoplasticelastomers for medical fluid delivery applications, including bags and tubing.

The new technology makes it possible to fasten non-halogenated,non-phthalate thermoplastic elastomers (TPEs) through a modified radiofrequency (RF) welding process.

"With ecoGenesis, manufacturers can use materials such asPolyOne's Versaflex TPEs in RF welding just like PVC, often providing improvedcost savings and a more environmentally friendly product," says Tom Ryder,chief executive officer for GenesisPlastics Welding of Fortville, IN.

The new technology dispels the common misperception that onlypolymers like PVC and polyurethane can be RF welded.

In radio frequency welding, which has been used since the1940s, two pieces of material are placed on a table press that applies pressureto both surface areas. Dies direct the welding process in which high-frequencywaves (usually 27.12 MHz) are passed through a small area between the die andthe table where the weld takes place. The RF field heats the molecules. Thecombination of the heat and the pressure bonds the materials.

Radio frequency welds from the inside out by focusing high-frequencyradio waves through an electrode die, rapidly generating complex welds in asingle stroke of an RF press. The process creates welds often as strong as orstronger than the material itself.

Only materials with a dielectric loss factor greater than0.02 (such as PVC and polyurethane) react to RF energy at the traditionallyused frequency. Plastics such as polyolefins are incapable of reacting toconventional RF energy because their dielectric loss factors are below 0.02.Dielectric loss refers to the proportion of energy lost as heat.

Converters have had to rely on alternative heat-seal systemswhich, by applying external heat, seal materials by melting from the outsidein. Unlike RF, most heat-seal systems are limited to straight line welds.

Other solutions that have been developed requiremodifications to the non-polar film. This includes using additives like ethylenevinyl acetate at a level high enough to raise the overall dielectric constantof the material above 0.02. According to Ryder, this method is more expensive,degrades the base polymer qualities, can create difficulties within the RFmanufacturing process, and requires external heat to be applied through theelectrode die in order to obtain a weld.

ecoGenesis is a proprietary "bolt-on" technology that enablesRF machines to weld polymers with dielectric constants below the 0.02 level. Theprocess incorporates a mechanical catalyst that makes RF energy visible tonon-polar materials and weldable in a number of substrates, including film,foam, wovens, non-wovens and more.

Ryder says that ecoGenesis enables the RF to rapidly heatthe polymer and generate the same uniform weld strength and appearance. Thisincludes polyethylene, polypropylene, PET and many other low-loss materials.Unlike RF buffer technologies, ecoGenesis is capable of tear seal RF welding,which is critical in mainstream RF welding applications to maximize efficiencyin production.

One of the advantages of TPEs is that thinner gauges canprovide the same feel and texture as thicker gauges of traditional materials,thereby lowering system costs.

PolyOne did not modify its materials to work with ecoGenesis,but did work with Genesis in fine-tuning its process and to help verify thatthe sealing performance met requirements for medical applications.