Analysis of failure causes of epoxy-phenolic coated tinplate after boiling sterilization

This work aimed to study the "blushing" phenomenon occurring on epoxy-phenolic coated tinplate after boiling sterilization at 127 celcius for 1 h. The corrosion resistance of the "blushing" coating and intact coating were measured in NaCl solutions. The possible failure causes were investigated by electrochemical impedance spectroscopy (EIS) combined with surface and crosssection morphology analyses. Electrochemical equivalent circuit (EEC) analyses revealed that, the coating resistance of the "whitening" sample was 6 times lower than the intact sample, while the charge transfer resistance at the tinplate/coating interface of the "whitening" sample was 10 times lower than the intact sample. The capacitance arc at low frequency range showed a constant phase element (CPE) behavior (a time constant dispersion at the tinplate/coating interface), which was due to the material composition inhomogeneity at that interface. Severe underfilm corrosion and coating disbondment were observed on the "whitening" sample after immersing into NaCl solution for 3d, which was due to the poor anticorrosion resistance of the epoxy-phenolic coating and poor coating adhesion. Thin thickness, poor adhesion and disbondment led to a "white" appearance after boiling sterilization.