Strategies to optimise organic coating systems

Description

Organic coatings are generally used for metal protection. The coating process involves several steps, which can be summarised as follows: (i) metal cleaning, (ii) chemical pretreatment, (iii) passivation, (iv) priming and (v) application of top coats. Electrochemical Impedance Spectroscopy (EIS) is a valuable tool to tailor each step and/or optimise the protective performances of the complete coating system. EIS on deformed, T-bent and damaged samples of complete systems can be used as a tool to obtain a selective evaluation of the best chemical pretreatment/primer combinations. Impedance data analysis and equivalent circuit modelling on undamaged and artificially damaged coatings exposed to aggressive environments can be used to evaluate the influence of formulation parameters, as Pigment Volume Concentration (PVC), on the protective performance and the retention of the coating adhesion, respectively. EIS data obtained for intact coatings can be analysed to evaluate water permeability coefficients, often influenced by the molecular weight and the chemical nature of the resins constituting the coatings. Several case histories will be presented to gain further insight on the power of EIS for the optimisation of organic coating systems.

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