Fiber laser process targets medical plastics welding

A powerful laser technology originally developed for the telecommunications industry is now targeting plastic welding, and has significant implications for medical markets because it eliminates use of dyes and other additive extractables. It may also expedite the welding of polyolefin elastomers that are bidding to replace polyvinyl chloride (PVC) for intravenous tubing and bags.

The technology, developed in Russia in the 1990s by academic researchers, was introduced at NPE2012 and discussed in a presentation at Antec by IPG Photonics (Oxford, MA), which had never exhibited at NPE before but now views nonmetallic welding as one of its biggest growth areas.

The melt zone is visible in 20 layers of 0.1-mm-thick LDPE welded with 90 watts of laser power at 1940 nm. Source: IPG Photonics

"One of the limitations of traditional laser welding is that you had to have a clear and a colored material for the laser to work," a processor told PlasticsToday after being asked what he thought was the most interesting new sealing technology he saw at the show. "IPG Photonics has figured out a way to seal clear materials."

A different approach

The new approach is based on fiber lasers that use semiconductor diodes as the light source to pump specialty optical fibers, which are infused with rare earth ions. "Fiber lasers are not fiber-delivered lasers," Tony Hoult, general manager - West Coast operations for IPG Photonics, told PlasticsToday in an interview.

In traditional laser technology, developed more than 50 years ago, an energy source excites or pumps a lasing medium that produces laser photons of a particular wavelength; when focused this causes melting of the target material. The two primary types are named for the materials used to create the lasing action: CO 2 gas lasers and crystal lasers. The most common crystal lasers use yttrium aluminum garnet—YAG crystals infused with neodymium.

IPG Photonics is targeting plastics welding for medical devices with thulium fiber laser systems that operate in the spectral range of 1800 to 2100 nm. A 1940-nm system was demonstrated at NPE2012.

"At this wave length you get more absorption in almost all clear polymers because the wavelength is closer to some vibration frequencies of the carbon-hydrogen bond (in plastics)," Hoult said in the interview. "When you bond polymers, you want something between 0 and 100% absorption and that's what you get with the thulium fiber laser."

No modifications required

One of the benefits to this welding technique is that no material modifications or additional infra-red

absorbing layers are necessary to improve the absorption of the laser beam in the polymer. The reason is that the absorption of the laser beam is taking place in the bulk of the polymer, not just at the surface or at the interface.

Samples at NPE2012 showed 2-mm-thick polycarbonate welded at 30 mm/sec at 80 watts. Source: IPG Photonics

When conventional near infra-red lasers are used, no controlled melting of clear polymers is possible unless specific infra-red absorbers such as the Clearweld infra-red absorbing inks or the Lumogen or Lazerflair dyes are used. Clearweld inks add cost and require separate

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