An Investigation on the Cathodic Disbonding Behavior of Polyurethane Coating Containing a New Generation Phosphate-based Pigment

In recent years، attempts have been done to replace toxic materials like chromate based pigments by phosphate pigments having less toxicity properties. However، the anticorrosive performance of zinc phosphate pigment has been proven not to be comparable to chromate type pigments. Regarding this، attempts have done to produce second generation of phosphate pigments. This study aims to investigate and compare the properties of a polyurethane coating، containing zinc phosphate (ZP: first generationpigments) and zinc aluminum phosphate (ZPA: second generation)، at different pigment volume concentrations (PVC) of each pigment. Effect of pigment type as well as PVC on the adhesion of coating to steel panels were investigated before and after 90 days immersion in 3. 5 wt% NaCl solution using pull-off test. Cathodic disbonding (CD) was done according to ASTM G8 to investigate the disbonding behavior of coatings. Results obtained in pull-off and Cathodic disbonding (CD) tests revealed that، greater adhesion loss can be observed on the samples showing lower resistance against disbonding. Evaluation of coating resistances against disbonding were examined at each of the PVCs. It was found that، the solved components of each pigment، at their optimum PVCs، can produce protective layer at coating/metal interface which lead to increase resistance of coated layer to disbonding.