Laser sealing for packaging films – suitable for any contour and established materials

The packaging of consumer goods as well as the manufacturing of technical products with film-based wrapping put increasingly great demands on the format flexibility and tightness of the sealed seams. The most conventional constant heat sealing system as well as the ultrasonic sealing mainly requires sealing layers made of diverse polyethylene. These have limited tightness properties compared with the barrier function of modern composite films and are opposed to a material reduction within the packaging film. Furthermore the named processes are format-dependent. Laser technologies, like the laser transmission sealing, are able to overcome the restrictions. However, thus far its use failed due to the need to integrate the radiation absorbers into the films because especially using only the widespread transparent films results in insufficient absorption of the laser light. This fact would increase the price of these films significantly, make its worldwide availability difficult and will minimize the acceptance of the laser as a sealing device. Last but not least the high acquisition costs were criteria against the use of laser systems in the past.

A new technological approach of laser joining through the use of a new generation of diode laser beam sources is the aim of a joint project between the Fraunhofer IVV, Branch Lab for Processing Machinery and Packaging Technology (AVV) in Dresden and the Fraunhofer Institute for Laser Technology ILT in Aachen. The energy for fusing the films will be deposited in an area smaller than 10 microns within the joining area. It is possible to achieve the following benefits by using a wavelength that is adapted to a characteristic absorption resonance of packaging polymers and a dynamic local laser modulation as well as a process-optimized beam guiding:

• The sealing of commercially available packaging films can be achieved for the first time.
• The seam contour can be designed flexibly.
• The thickness of the sealing layer can be reduced or the sealing layer may be eliminated.
• The energy deposition, the seam resistance and the process velocity can be influenced selectively.
• A laser system can be created which is competitively priced relative to its benefits.

Within the project a demonstrator test rig has been developed and assembled to verify the technology. Consequently there is the potential to modify the parameters for different applications and material combinations. An inline quality control will also be integrated, facilitating a systematic investigation of the laser sealing mechanisms. The technology can be tested on industrial applications and can be made usable for potential clients.

The technology is aimed at the packaging of food, cosmetics, drugs and medical devices as well as the manufacturing of technical products currently probable in a higher price sector. The user will be the packaging industry, the supplier industry and the machine manufacturer. These will help to transfer the technology in other industrial sectors, for example in plastic and building techniques.