Heat Sealing Paper with Polymer Film

This thesis concentrated on studying heat sealing paper with polymer film by hot-bar sealing. The objectives included learning more about the relationship of the materials and how they behave in different heat sealing conditions. Also some methods were tested out for heat sealed samples to find out if they would provide useful information because one interest was to find new methods for testing. Theory part introduces flexible paper-polymer films packages that are opened by peeling. Also the heat sealing process and the method to measure seal strength have been presented. Adhesion theories that are the most applicable considering heat sealing have been introduced. It was found that sealing temperature affects seal properties greatly. When certain level of pressure is applied, it doesn’t affect seal strength notably anymore if it’s increased. Correlation between seal strength and fibre amount index was found not to be straight forward. Results suggested that pressure effects on the peel characteristics so that high pressure possibly makes the paper surface more compact and molten polymer doesn’t flow into valleys and voids of paper’s surface thus giving smaller fibre amount index. With profilometer it was possible to obtain differences to the surface roughness for samples heat sealed with different parameter and the images showed clearly the fibres that were pointing out of paper surface and attached to polymer film. When comparing manual peeling to using an instrument it was found that with the instrument fibre amount index levels were higher but standard deviations were not smaller