Absorbing dye joins plastics invisibly

17 Jun 2002

An organic dye that absorbs infrared light allows plastics to be welded together with joins that are almost invisible to the human eye.

The process, developed by TWI in Cambridge, UK, exploits an infrared-absorbing dye from Gentex in the US.

Usually, transmission laser welding requires one of the layers to contain a black absorber, such as carbon black. This makes the join unsightly and so inappropriate for applications like packaging, optical products and fabrics. The new technique allows two clear plastics to be joined.

The dye is applied between two layers of the plastic and a 1064 nanometre laser beam is shone through the top layer. The dye absorbs the energy from the beam, generating heat that welds the two plastic layers together. Sue Dunkerton, head of Advanced Materials and Processes at TWI, says that the heat is very localized so there is no thermal degradation or material disruption surrounding the join. She adds that initial tests show that the bond formed is leak tight.

Dunkerton believes that products will emerge from this technique within about a year.

TWI will be presenting a paper on this technology at the Laser Institute of America's ICALEO meeting in California next month.

SH