Probably one of the most influential patents on laser welding of plastics is a patent EP 0 751 865 first filed by Marquardt GmbH in 1994. It protects the welding of two workpiece parts using the transmission method, which have the same color in the visible light spectrum.
Technically, the idea and implementation with the then still young welding process was a milestone. Laser welding of plastics using the transmission method requires two workpiece parts with different optical properties in the range of the wavelength of the processing laser. Until this invention, this meant that they inevitably had a different color impression even in the visible wavelength spectrum. This was often an undesirable effect.
The invention made it possible for the first time to join two workpiece parts that appeared black to the human eye. This overcame entry hurdles in the innovation-driven automotive industry, and laser welding was able to establish itself there in many areas. One of the first applications produced using this new process was a vehicle key for a German luxury brand. Today, the patent has lost its validity, welding plastics of the same color with the laser is state of the art and it is used in hundreds of applications worldwide.