Adhesion improvement of the UV lacquers for food cans by applying a post-curing current treatment

In this work, we investigated three different ways of improving, in a cycloaliphatic epoxide-based UV lacquer, adhesion to industrially coated tinplate: modification of the tinplate passivation film composition, post-curing thermal treatment of the UV lacquer and cathodic current application to lacquered samples.First, the characteristics of the tinplate passivation film were considered by producing different chromium-based films on an industrial line at low, medium and high pH values and various charge densities (0–5 C/dm2).Second, some tinplate sheets of each material were baked in an oven at 200 °C for 15 min in order to study also the influence of a post-curing thermal treatment on lacquer adhesion to metallic substrate. The adhesion properties of baked and non-baked samples were investigated by means of dry adhesion, wet adhesion in citric solution at pH 3 and electrochemical impedance spectroscopy (EIS) in a phosphate buffer solution at pH 6.Finally, the effect of cathodic polarisation (−2 V for 1 min) on non-baked samples was checked by using EIS (AC/DC/AC technique).The additional UV lacquer reticulation by the current passage, detected using EIS technique, was supported by statistical analysis and reflectance-mode FT-IR microscopy.