Tinplate Corrosion Under a BPA-NI Polyester Lacquer

Bisphenol A-Non Intent (BPA-NI) lacquers such as polyester and acrylics are replacing the epoxy-phenolic lacquer in the sanitary food cans. Occasional lacquer failures have been reported on cans using the BPA-NI lacquer, but the root cause of the failure was not fully understood. In this study, the corrosion behavior of the tinplate coated with a polyester lacquer was examined in three different environments to understand the corrosion mechanism under the lacquer. The study suggests a different corrosion mechanism for the lacquered tinplate and plain tinplate. Under the lacquer coating, tinplate corrosion starts with detinning to expose FeSn 2 alloy layer, which is followed by iron corrosion in the pores of the alloy layer where the steel substrate is exposed. The corrosion rate of the tinplate under the lacquer can be influenced by the severity of the environment, Sn coating weights and surface cleanliness of the tinplate.