As a powder coating is subjected to heat, its cure proceeds along various stages.
Stage 1: Melt Point
Powder particles begin changing from a solid to semi-liquid state.
Stage 2: Flow Stage
Powder is fully liquefied, reaching lowest viscosity, allowing the film to smooth out.
Stage 3: Cross Linking Stage
Sufficient, sustained heat triggers large scale reaction within film; this reaction is the initial step to total chemical and physical change of product.
Stage 4: Gel Stage
At the point when sufficient crosslinking has occurred, solidification of the film takes place.
Stage 5: Cure Development
The final and most critical stage: baking. Baking causes a reaction of majority of crosslinking sites and development of optimal film properties.
Stage 6: Over Cure
The film will start to lose some flexibility turning yellow in color with potentially decreased gloss below expected levels. Inter-coat adhesion is compromised and catastrophic failures become likely.