Where the
world gathers for metal finishing
Q&As since 1989


-----

Salt tracking problem with PVC plastisol

Dear board,
I am a Vinyl plastisol development Chemist at a USA chemical company. I have been recently assigned the task of removing the salt tracking lines left on plastisol coatings after parts are removed from a molten salt (Sodium Nitrite) tank. I have tried everything from Hydrolysis preventers to Parradfin waxes to different plasticiser and resin combinations no avail. I have a competitors sample and it does not exhibit this phenomenon. The process by which this plastisol is processed is: Parts are cleaned in a Caustic wash to remove any dirt grime or mill scale, then washed clean, then dried, then primed, then preheated to 450F, then dipped into my plastisol for a period of 30 seconds, then removed slowly to reduce drips and allowed to drip free and pre gel, then they are dipped into 395F molten salt for a period of 2 minutes, then removed to drip free, then the parts are ran through a wash stage to remove the crystalized salt from the part, then you have a finished part. Only problem is that my plastisol formulation after being washed leaves "salt track" lines, where salt had sat waiting to be washed off the part. I have talked to some of the greatest minds in this business and they all say no idea. Any thoughts or suggestions would be greatly appreciated.

Chris Pontius
- St Louis, Missouri
2006