Tin plated steel sheets have discoloration during curing of coating

[Tebza33]

Hi

I presently have a problem with tin plated sheets showing discoloration during curing of the coating material inside the oven.
Current temperature settings on the oven only go up to 200 degrees celcius and they are heated for approx 12 minutes. My question
is can temperature variations affect the tin to a point where it may possess a plastic phase? Or is this discoloration due to excessive
temperatures over-curing the coating and hence the proof of discoloration?

I have tried to remove the coating material on a discolored sheet by means of a solvent, and the discoloration is still visible. But when a
raw sheet is being put through the oven, there is no discoloration. This can suggest that over-curing may form a different kind of compound that
has adhered onto the tin, and is immune to the solvent being used! Maximum oven temperature (design) is 250 degrees, but we have measures in place
to control it at the set point.

 

[Compositepro]

200C is a very high cure temperature for most paints. It can be done to get a fast heat-up and cure but then time at temperature must be carefully controlled to avoid darkening of the resin binder in the paint due to oxidation. Tin compounds are also cure catalysts for many paint chemistries.