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Unique Welding Process Expands TPE Use

Unique Welding Process Expands TPE Use

A breakthrough assembly technology opens the use of thermoplastic elastomers 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 radio frequency (RF) welding process.

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

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

In radio frequency welding, which has been used since the 1940s, two pieces of material are placed on a table press that applies pressure to both surface areas. Dies direct the welding process in which high-frequency waves (usually 27.12 MHz) are passed through a small area between the die and the table where the weld takes place. The RF field heats the molecules. The combination of the heat and the pressure bonds the materials.

Unique Welding Process Expands TPE Use

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

Only materials with a dielectric loss factor greater than 0.02 (such as PVC and polyurethane) react to RF energy at the traditionally used frequency. Plastics such as polyolefins are incapable of reacting to conventional 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 systems which, by applying external heat, seal materials by melting from the outside in. Unlike RF, most heat-seal systems are limited to straight line welds.

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

ecoGenesis is a proprietary "bolt-on" technology that enables RF machines to weld polymers with dielectric constants below the 0.02 level. The process incorporates a mechanical catalyst that makes RF energy visible to non-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 heat the polymer and generate the same uniform weld strength and appearance. This includes 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 efficiency in production.

One of the advantages of TPEs is that thinner gauges can provide 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 that the sealing performance met requirements for medical applications.
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