Influence of Reverse Electrolysis on Lacquer Adhesivity of Tin Free Steel

Abstract

The application of anodic (reverse) electrolysis to the 2 step process of tin free steel has brought the improvement of lacquer adhesivity during retort treatment. This new process consists of chromium plating, reverse electrolysis and chemical treatment.
It was found that the reduction of anions (sulfate ions, fluoride ions) and the uniform thickness of the Cr-oxide layer of tin free steel were necessary to good lacquer adhesivity. The steel after the chromium plating has a Cr-oxide layer with a lot of anions and uneven thickness. The reverse electrolysis removes the upper anion rich part of the Cr-oxide layer. Furthermore the chemical treatment in a CrO₃ bath without anion addition forms a uniform Cr-oxide layer with less anions providing good lacuer adhesivity.