Today, it is widely believed that laser welding of plastics was invented around the turn of the millennium. However, old patents and patent applications in particular show that the technology was considered and also used much earlier.
For example, Mobil Oil Corporation applied for patent US 3,560,261 in 1964 and it was granted in 1971. The patent, entitled “Bonding thermoplastic plastic films by means of radiation from a laser source,” describes the bonding of films by means of a laser. In addition to detailed explanations of the structure and procedure of the welding process, the patent also provides an outlook on the technical possibilities of the then new process. In this context, not only films are named as an area of application, but also entire molded parts with wall thicknesses of several millimeters.
The patented process is not the transmission welding process often used today with two differently absorbing joining partners. Rather, it is similar to so-called 2µm welding, which is based on volume absorption. Since the aim was to avoid deformation and melting of the surfaces, attempts were already made at that time to use optical elements to place the energy input as close as possible to the interface between the two joining partners. This technology is still used today. Since 1964, many different patents have been filed and granted around the technology of laser welding of plastics. In this blog, we will take a closer look at one or the other significant patent and its technical relevance in the coming months.