Laser transmission welding of aluminum film coated with heat sealable co-polyester resin with polypropylene films for applications in food and drug packaging

Abstract

The present work deals with the high-power diode laser joining process of aluminum films coated with a polyester resin with polypropylene (PP) films. The first part of the work focused on analyzing the coating process of aluminum films with a polyester resin, using an automatic applicator. The second part of the work was focused on the analysis of the laser joining process of coated aluminum films with plastic counterparts made of PP. Different thicknesses and colors of the PP parts were tested in order to analyze the joining process under a wide range of different conditions. The experimental plan involved the study of the influence of the laser joining parameters, in particular the scanning speed and beam power, on the joints. The joints between aluminum and PP films were subsequently tested by means of tensile and peel-off tests. All the joints between aluminum and PP are obtained through the so-called laser transmission welding (LTW) mechanism. Analysis of the mechanical response of the welded joints allowed to identify the optimal processing window, that is, the choice of the operational parameters that leads to satisfactory welded joints, stating the high potential of laser systems in the joining process of aluminum and PP films for food packaging applications.

Shelf-life, bioburden, water and oxygen permeability studies of laser welded SEBS/PP blended polymer

“…However, as a whole, the topmost transparent SEBS/PP polymer film cannot effectively absorb the heat, necessitating a high number of scans and flipping of the irradiated surface 43 . In addition, as a non-excessive force was applied to clamp down the polymer sandwich, the force applied on the sample, the molten material is pressed out of the joining zone 44 .…”

“…Therefore, no excess material is pushed to the surfaces to create bead-like material on the surface. Parameters beyond the optimized range would mean working with laser radiation transmitted towards the surface that is too low or high, leading to ineffective welding or potentially to polymer degradation 43 .…”

“…In addition to that, due to the low power, the laser was not able to sufficiently penetrate the depth of the polymer. Therefore, at low laser beam powers, a stably welded joint cannot form, and the joint resistance is consequently zero 43 , 46 . In this instance, the laser radiated on the joint interface could not initiate the polymer's melting at the interface.…”

“…This characteristic indicates that the polymer is softened with the increase of time 44 . Furthermore, setting the laser beam with high power leads to erstwhile shrinkage or wrinkling 43 . The rapid heating and cooling due to the thermal expansion of the polymer film surface in the molten state when irradiated and the rapid contraction following its cooling after the laser beam has passed thereof leads to surface wrinkling or shrinkage.…”

Optimization of Laser-Assisted Polypropylene Aluminum Joining

“…There are few studies available on the laser joining of Al and PP, for example, [21] reports on the application of a polar insert material between Al and PP, and [22] uses a polyester resin to coat Al before laser joining to PP for applications in food and drug packaging. In another study, the mindset of using PP in the laser joining process is merely to eliminate the physicochemical interaction with the Al surface and study the melting layer of PP during the joining process [8].…”