Finish issues/gun blush


ed_mines
 

the defect is called gun blush and it occurs when moisture condenses on solvent borne coatings that are drying.

When liquids evaporate they pull heat out of their surroundings so those surroundings and the coating surface get cool. When this temperature goes below the dew point gun blush forms.
This defect is more likely to occur if coatings contain fast drying solvents like acetone. If slower solvents are used as thinners the coating takes longer to dry and the localized temperature doesn't drop so much.

Why adjacent to the decals? Maybe the coating pooled in this area.

The defect can sometimes be corrected by redissolving the coating surface. I told customers to respray the coating with a slower evaporating thinner like xylene. Sometimes that worked.

Maybe the decal setting solution redissolved the coating.

Using light, dusting coats of coating that don't stay wet very long can help avoid this problem. So can using a slower evaporating thinner.

My employer had a similar problem with aerosol cans of acrylic coating. We made the coating and an outside company put it in aerosol cans. They changed one of the solvents for health and safety reasons.