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Tin-plate and tin free steel are commonly treated with a sodium dichromate solution before the coating is applied. This stabilizes and prepares the metal surface to receive the coating and inhibits rust. However, PPG has products that work well on cleaned-only substrates. Because of environmental concerns about use of chromium, many can makers and coil coaters prefer using cleaned-only substrates rather than chrome-treated ones.
With this in mind, PPG works on lacquer projects where the specification includes application to cleaned-only or non-chrome-treated substrates. PPG will design a system that meets the can maker's concerns for chrome-free pretreatment while resulting in the needed performance characteristics.
A unique solution is the patented electro-coat process for easy-open beer can ends that requires no added pretreatment. The coating is applied via the anodic electrodeposition process, by which aluminum oxide is formed concurrently with coating deposition electrochemically, forming the strong adhesion between the aluminum substrate and the PPG coating.
Nearly 300 billion beer can ends have been coated with PPG's electro-coat by Alcoa for more than 16 years.