Fractal dimensions of blast-cleaned steel surfaces and their effects on the adhesion of polymeric foil systems with integrated pressure-sensitive adhesives

Abstract

Morphology and structure of substrate surfaces are crucial parameters for the establishment of reliable protective layers as they determine the adhesion of the protective layer to the substrate. Insufficient adhesion will promote unwanted effects, namely delamination and blistering. This applies as well to protective hybrid-layers, consisting of a polymeric foil bonded to the substrate (usually steel) by means of an integrated pressure-sensitive adhesive. Numerous parameters are known to characterize the morphology of metal substrates. In this study, mild steel samples were prepared using dry-blast cleaning with abrasive materials (metallic, minerals) of different particle shapes and particle sizes to investigate the impact of surface profile parameters on the adhesion of polymeric foil systems (PFS). For this purpose, 2D profiles were taken from a total of 12 surface configurations with a digital contact profilometer. Fractal dimensions were estimated based on these recorded profiles using the box-counting method. For comparison, conventional roughness parameters were measured as well. Tests with a pull-off strength testing device were performed on the applied PFS to quantify its adhesion to the substrates. The estimated pull-off tensile strength values were correlated with the estimated fractal dimensions. Design of Experiment (DoE) was applied to the test design in order to establish statistically sound relationships. Using a linear correlation model, it could be shown that fractal dimensions were suitable for quantifying the adhesion with a significantly higher accuracy than commonly used substrate (roughness) parameters.