Understanding Seal Integrity - Sealing and Closing of Flexible Packaging
Ilknur Ilhan is a PhD student in the department Advanced Manufacturing, Sustainable Products & Energy Systems. Supervisors are prof.dr. I. Gibson and prof.dr.ir. R. ten Klooster from the faculty of Engineering Technology.
Condition of heat seal region in flexible food packaging is decisive to preserve food quality along the shelf life. The main process parameters of heat sealing, namingly time, temperature, and pressure are adjusted by manufacturers based on the characteristics of the film being used. Nonetheless, issues with seal integrity are still encountered. This thesis aims to understand the mechanisms that lead to problems in the heat sealing process of flexible packaging and to identify ways of preventing seal integrity issues. It explores various factors that can impact the quality of heat seal in different types of conventional flexible films.
The research findings indicate that there are many different material properties, process parameters, contaminants, and future processes that can contribute to the formation of gaps and micro-leakages in the seal area, and these parameters can be interrelated. To understand the relationships between these parameters and their impact on the leak formation, some chosen parameters such as contaminant food particles, film tension, melt flow index (MFI), seal bar design, and filler ratio are experimentally investigated. Through the experimental research, first, it is determined that the maximum acceptable density of solid food particle contamination in the seal area varies based on particle size, and is lower for fine, dusty particles. Then, it is confirmed that the design of the seal bar can affect seal strength and integrity, and it should be modified to optimize the pressure distribution along the seal. Next to that, pressure fluctuation that occurs along the seal because of package design is examined and its impacts on seal quality and wrinkle formation are shown. Moreover, the importance of the composition of the film and sealant material for determining the optimal sealing temperature and dwell time is presented along with a method to optimize the main process parameters; time, temperature and pressure. And finally, the effects of investigated parameters on easy-peel function as packaging requirement are elaborated. It is indicated that an easy-peel function can be achieved by a more precise optimization of sealing time and temperature, avoiding excessive pressure that can occur due to the layer jumps, adjusting MFI of the sealant and eliminating film tension during sealing.
Overall, this thesis takes a step towards grasping the mechanisms that can cause leaks in the seal area of flexible food packaging. It brings suggestions to cope with the complexity of various parameters that affect the seal quality and takes in to account achieving different packaging requirements such as easy peeling.