Influence of side stripe on the corrosion of unlacquered tinplate cans for food preserves

Abstract

Metal containers are used for packaging foodstuffs; more specifically, the cans used for preserving fruit have a plain body with side seam protected by a lacquer film. The traditionally used side stripe is adopted “out of abundance of caution”, as the tin present on the seam is removed by the welding process. Not using a side stripe would have practical/functional benefits for the entire production chain, with consequent reduction in the cost of the containers and in their environmental impact. Packaging of medium‐acidity products in tinplate cans is based on the principle of cathodic protection of steel by tin. To ensure that this condition persists throughout the product's shelf life, it is necessary for the anode area to be larger than the cathode area. When the seam is protected with lacquer, this condition is met. In cans where no side stripe is applied on the inner seam, the cathode area increases; this could lead to an increase in corrosion rate and consequent reduction of shelf life. However, the use of tinplate with high tin coating weight (D 11.2 g/m2) can limit this effect, under suitable packaging conditions (absence of oxygen). The aim of this study is to analyze the possibility of using cans without lacquer stripe on the electric side seam for the packaging of fruit and, more generally, of medium‐acidity products. Electrochemical measurements of model‐systems, and pack tests were used in the study.

Surface coverage characterization of tinplates after post‐treatment processes

“…Tinplate finds its main application in containers for packaging [1]. The manufacturing process of these cans includes a cylindrical body produced by forming rectangular blanks around a mandrel and soldering (now increasingly rare), resistance welding, or occasionally cementing the side seam [2][3][4][5]. Soldering changes the state of the tin coating and welding modifies the steel near the weld.…”

“…Soldering changes the state of the tin coating and welding modifies the steel near the weld. Both welding and cementing can produce lap joints that may have exposed edges and the possibility of crevices [3]. Moreover, the tinplate surface may undergo major deformation with disruption of the tin coating.…”

“…Moreover, the tinplate surface may undergo major deformation with disruption of the tin coating. Therefore, the can manufacturing processes can change the nature of the tinplate material and thus influence its corrosion [3]. Besides, tinplate itself is metallic coating system, and during corrosion process, tin coating acts protectively and the steel dissolution is suppressed with the loss of tin being the corrosion reaction encountered [3].…”

“…Therefore, the can manufacturing processes can change the nature of the tinplate material and thus influence its corrosion [3]. Besides, tinplate itself is metallic coating system, and during corrosion process, tin coating acts protectively and the steel dissolution is suppressed with the loss of tin being the corrosion reaction encountered [3]. Therefore, the integrity and uniformity of tin coating on tinplate surface are also essential for the protective effect of the underlying steel sheet.…”

Investigation and mechanism of headspace corrosion in metal cans filled chicken noodle soup

“…These coatings are applied as an internal organic lining over the base metal in order to provide an inert barrier between the metal and the food product. 6 Because of its excellent toughness, corrosion resistivity and high adhesive properties to metals, epoxy resin became a perfect material to coat food cans. 7 Huang et al 8 reported that in 2011, 5.5 million tons of BPA were produced, making it one of the world's most abundantly produced industrial chemical at that time.…”