Imaging Methods for Analyzing Adhesion in Extrusion Coating

Abstract

Extrusion coating is a common method to produce materials for the packaging industry. One of the most important properties in extrusion-coated structures is adhesion between the substrate and the coating. Analyzing adhesion of samples produced by extrusion coating in a standardized way can be challenging, and especially, quantitative data are often hard to obtain. A commonly used method is visual adhesion evaluation. The object of this research is to present how different imaging methods can be used as a support to visual evaluation by obtaining more profound information. Other aspects looked into are the possibility of studying how adhesion is affected by adjusting process parameters during the coating process or using modified paperboard substrates. The samples studied in this research are different paperboard substrates coated with polyethylene or polyethylene terephthalate. Optical microscopy, profilometry, and X-ray microtomography are used to image selected samples. The results show that versatile information can be obtained, for example, about the intensity of physical contact between the layers, the type of bonding occurred, and effects of the nature of the substrate surface.