Melt Detection

Strategies to improve the recycling of polymer-based packaging are the substitution of conventional multilayer films by mono-polyolefin films and an increased fraction of recycled material in packaging films. However, these films show a significantly smaller sealing range and changed processing properties during sealing. To secure the packaging’s quality despite higher requirements, increases the necessity for a close coordination between material, process and machine parameters.

The formation of a polymer melt to join the films along the sealed seam is crucial for the production of high quality sealed seams. Therefore, the film’s thermoplastic sealing layer must reach a molten state. This correlation is described by viscosity. Furthermore, the melt’s viscosity influences the structure and orientation of the molecule chains in the seam area and hence the seam quality. However, there is currently no detection possibility of the sealing layer’s viscosity during the sealing process.

The Fraunhofer IVV’s approach is to monitor the polymer melt’s viscosity during sealing by ultrasonic sensors. The sensor’s acoustic measurement signal enables the detection of the melt viscosity due to a change in velocity of sound depending on the material density.

To provide a proof of concept, this IVLV project’s scope is the development of a sealing tool to measure the sealing layer’s viscosity by ultrasonic sensors. For this, an experimental set up is realized to integrate the sensors in the heat-sealing process and thus different measurement methods are compared. The approach’s potential to detect the formation of melt during the sealing process is estimated by the anal-ysis of the senor data and the derivation of first correlations to material data measured in the lab. Furthermore, possible application fields are identified.

By capturing the melt viscosity as a measured variable, conclusions will be enabled about the seam quality during the process, taking also into account the material properties to increase the process stability and hence the product safety by an adaptive adjustment of sealing parameters in the future.