Short answer
Almost always the cause is surface contamination from release agent, above all silicone, transferring to the part. Use paintable, non-silicone release grades, confirm contamination with a water-break or dyne test, and keep silicone sprays out of the production area altogether.
Likely causes
Silicone release agent or silicone spray
Used on the line, or airborne or carried on gloves and wipes from another area.
Heavy transfer of release film
Especially with wax pastes.
Smooth, fully skinned surface
Little mechanical key for the coating.
Paint or primer mismatch
Not matched to the PU surface.
How to diagnose it
- Water-break test: does water sheet out or bead up on the part?
- Dyne pen test and cross-hatch tape pull.
- Trace every silicone product in the plant.
How to fix it
- Move to a paintable release grade.
- Solvent-wipe parts before coating, and use plasma, flame or primer where needed.
- Remove silicone products from the production environment.
How to stop it coming back
- Segregate and label silicone products.
- Tell the paint shop which release agent was used on every lot.
Where this problem appears most
Send us your batch number, PU system and a photo of the defect and our technical team will help you trace the cause. Ask a technical question.
