A New, Chrome-Free Passivation Method of Tinplate Used in the Canning Industry

Abstract

Tinplate is used widely in the canning industry. Its passivation treatment involves mainly the use of chromium, and it is applied typically with the cathodic dichromate (CDC) procedure. The present study provided evidence by means of laboratory testing in aerobic and anaerobic conditions that the combination of an acrylic copolymer with an active pigment based on fluorozirconic acid is a viable alternative to the traditional CDC method for the passivation of tinplate used in the canning industry. The method is environmentally friendly and comprises easy application and cost-saving by avoiding rinsing and current. The principle of this method already has been applied successfully for the passivation of aluminum surfaces. Furthermore, based on x-ray photoelectron spectroscopy (XPS) investigations, a novel approach regarding the mechanism of corrosion inhibition on tinplate was presented and based on the formation of nanoparticles composed by an ideal tin core and a tin oxide surrounding. The long-term goal of this investigation is to develop a new, chrome-free, rinse-free, and cost-effective method for tinplate passivation. This method will provide an alternative to the chrome treatment (CDC), which is considered to be toxic for the environment (in the form of industrial wastes), as well as, above a certain limit, for the human consumer. The same or similar treatments in the future may be applied in low-tin steel (LTS) or tin-free steel (TFS).