Three types of steel - tinplate, chromium coated steel , black plate - are used in packaging steels.

Tinplate

Tinplate is a thin sheet or strip of soft steel, less than 0.50 mm thick, coated electrolytically on both sides with block tin.

Tinning is carried out by a continuous electrolytic process after degreasing and pickling operations which eliminate respectively the greasy residue of rolling and the oxide film covering the steel strip. To satisfy the different packaging functions, it is possible to obtain differential coatings : both sides of the strip are coated with a different quantity of tin.
After tin-plating, two new operations are carried out : remelting and passivation before the final oiling.
This operation fixes 2 layers of tin : the thicker exterior layer of only tin, called «free tin», and the thinner, interior layer of a tin / iron alloy, called «alloyed tin». This interior layer increases the steel’s resistance to galvanic corrosion due to its fine continuous structure.

Chromium coated steel

Chromium coated steel is a sheet or strip of steel coated with a layer of chrome less than a micron thick.

Chromium plating of steel for use in the food industry is done electrolytically in a chrome acid bath. Originally called TFS (Tin Free Steel), it is now known by the acronym, ECCS (Electrolytic Chromium Coated Steel). Process parameters (current density, temperature...) ensure the quality of the metal chrome deposition. The quantity of oxidized chrome is then fixed during a second stage called “washing”. This consists of excessive chemically washing of the oxidized chrome strip so as to obtain the required quantity.

With regard to its properties and use, ECCS possesses notable differences when compared with tinplated steel :

• ECCS is never used without any organic protection (lacquer, polymer) for food products. The lacquer provides lubrication in the production phase and protection against corrosion;
• Organic coatings generally have excellent adhesive properties on ECCS and are therefore used particularly for plated cans and standard food can bottoms.

Blackplate

Blackplate, a sheet or strip of steel with no coating, is the basic component of tinplate and ECCS, but in certain instances, it can be used as such, or covered with metallic or organic coatings.