Laser Welding with an Intermediate Film
The newly developed technique of laser welding with an intermediate film can bond incompatible thermoplastics that could not be bonded previously. Using this variant of laser transmission welding, it has been possible for the first time to weld PA12 parts to components of PBT, PP and PE.
The intermediate film technique is a variant of laser transmission welding that was developed at the Institute for Plastics Processing (IKV) at the RWTH Aachen. In this technique, the laser beam is absorbed by a film located between the surfaces to be welded. The laser beam plasticizes the film material. The actual weld is formed as the result of heat transfer that melts the materials on each side of the film.
With conventional laser transmission welding, one of the two materials to be welded always had to be pigmented in order to absorb the laser beam, since unfilled, unpigmented thermoplastics usually exhibit absorption to only a minimal degree. Use of the film replaces the absorbing pigment in one of the welded materials. The colour of the part can now be whatever is desired, so those even transparent welds are possible.
Moreover, the intermediate film technique permits welding of parts made of different materials. In this case, the absorbing film has a two-layer structure. One layer is the same material as one of the components to be welded, while the second layer is an adhesion promoter. The thickness of the multi-layer film is 100µm, with each layer having a thickness of 50µm.
This approach opens up new technical possibilities for a variety of different applications. By replacing relatively expensive materials, the materials costs can be reduced. The combination of different materials in a single part expands design freedom. In addition, standard thermoplastic resins can be used, since no special material modifications are needed. There is also the additional advantage that both of the components to be welded can be produced in the same mould or on the same injection moulding machine.