Electrolytic Tinplate undoubtedly enjoys the pride of place as a packaging medium especially for food. It owes its unique position to its "nine layer sandwich structure", each of which contributes to its eminence as a packing material. The steel base provides the necessary strength and formability for can fabrication. The tin-iron alloy layer provides the bond between the steel and free tin layer. The free tin layer is not only responsible for the attractive bright finish and ease of solderability but is also non-toxic- a factor of vital importance in food packaging!
Electrolytic TinPlate: Composition
E.T.P. consists of five layers each of which performs a different role:
1. Steel Base: Provides stiffness to the material due to its thickness and mechanical strength. Its chemical composition imparts special properties to resist corrosion.
2. Iron-Tin Alloy: This is made up by the inter-metallic compound Fe-Sn2. Due to its electrochemical characteristics, it acts as a barrier against corrosion. For effective action, its continuity is more important than its quantity.
3. Metallic Tin: Tin has many advantages which have turned it into the most important element to protect steel used for cans; in many foods, it acts as a simple barrier against corrosion, improves weldability, it is an excellent base for lithographic printing and for applying lacquers. In tin-robbing foods, it acts as a sacrificial element.
4. Passivation Film: According to its nature, it makes it possible to improve the E.T.P.’s resistance to sulphiding, oxidation and rust. It is also a conditioner to improve the adherence of varnishes, inks, lacquers etc.
5. Oil Film: Protects the sheet from the humidity in the environment and makes easy to handle. It is applied using an electrostatic oiler on both sides of the sheet.
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