Environmentally friendly coated tinplate for food cans

Dichromate passivation treatment has been the treatment of choice for tinplate for over fifty years. It provides excellent corrosion protection, very good lacquer backing and imparts good corrosion resistance to sulphide staining by certain foods. However the recognition that chromium in the hexavalent state is both toxic and carcinogenic has lead to a search for alternative non-toxic coating systems. In the first part of the work, at the industrial plant of Aceralia, Arcelor Group, Spain, was produced a coil of tinplate without the application of passivation treatment. This material was used as base material for producing Cr-free passivation treatments. Several Cr-free electrolytes were employed to produce passivation films on tinplate. The treatments using Ti-salt, Ce-salt, oxalate salt and Zr salt were carried out using the parameters selected during the laboratory experiments that are summarised in the following table: