Insufficient Structural-Sealant Compatibility
Silicone structural glazing sealants or weatherseals may wet the powder-coated surface poorly, appear bonded initially and then fail adhesively after ageing. The sealant may also remain bonded while pulling the powder coating away from the aluminium. Low surface energy, migrating additives, contamination, undercure and inadequate pretreatment can all contribute.
Formulation Design
- Minimise interference at the bonding interface from waxes, slip agents and other surface-migrating components.
- Subject to weathering and appearance requirements, select a polyester system with a stable surface condition and fix the gloss, colour and film thickness.
Process Control
- Validate compatibility using final powder-coated panels, the actual structural sealant and the specified sealant primer.
- Control cleaning, storage and cure after coating, preventing silicone oil, release agent and perspiration contamination in the bonding area.
- Test both the sealant-to-coating and coating-to-aluminium interfaces to identify the true failure location.
Validation Focus
- Peel/tensile adhesion
- Adhesion after damp heat
- Interfacial failure mode
- Sealant-primer compatibility