Sealing Paper Packaging Without Adhesives

Summary

After irradiation, fusible cleavage products remain on the paper surface and seal under heat and pressure without any additional material. “By irradiating the paper with a CO laser, we create refusible, sugar-like reaction products that we use instead of the synthetic materials or adhesives that would otherwise be required to seal the paper by the heat sealing process. In this way, we are essentially producing our own adhesive in the form of the cleavage products,” says Volker Franke, Group Manager Laser Micro Processing at Fraunhofer IWS in Dresden. “After laser treatment, we have succeeded in using heat sealing, an established thermal contact process, to bond two layers of paper with heat and pressure.” Bond strength defines seam quality The project partners at Fraunhofer IVV are developing the necessary sealing system for processing laser-treated papers with fusible cleavage products. To achieve this, the researchers are accounting for the effects of material properties, laser parameters and the properties of the fusible reaction products on bond strength based on data already recorded by the teams at Fraunhofer IAP and Fraunhofer IWS. They are also testing the extent to which bond strength and leak-tightness can be improved by using suitable sealing parameters and tool geometries and are transferring the results to a packaging solution with the goal of achieving seam properties suitable for the market. “Bond strength determines how difficult it is to tear open or to open packaging,” explains Fabian Kayatz, research scientist and project coordinator at Fraunhofer IVV in Dresden. “By measuring mechanical stability under different types of loads (shear test, T-peel test), we can demonstrate the effects of laser parameters and sealing parameters on the bond strength of the seams. Crucial sealing parameters are sealing time, sealing temperature, sealing pressure, and tool geometry. Fiber direction also plays a role, i.e., the orientation of the material relative to t...