New Methods for Determination of Coating Adhesion and Adhesion Degradation

The protectiveness of organic coatings depends to a large extent on the quality of the adhesion of the coatings to the substrate.  Various surface pretreatments are used to improve adhesion and coatings are developed for their high adhesion.  However, the techniques for quantitative assessment of adhesion strength are limited.  The most common approach is the pull-off strength of an adhesively-applied dolly, but this rarely results in complete adhesion loss, and the adhesive used to attach the dolly can influence the coating properties.  This talk will describe two methods for quantitative assessment of adhesion.  The first is the blister test in which the coating spanning a through-hole in the substrate is pressurized to form a blister.  The growth of the blister is monitored to assess coating adhesive energy.  The second approach is AFM scratching, in which a thin coating is delaminated by rastering the surface with an AFM tip in contact mode at constant tip force.  The tip force and number of rastering scans to completely remove a coating provide a measure of the coating adhesion.  These methods have been used to quantitatively assess the effects of pretreatments on AA2024 on the adhesion of coatings, and to determine the loss of adhesion of organic coatings on steel substrates as the result of exposure to corrosive conditions.