Common coil coating primer formulations are based on polyester resins heat cured with amino resins with acid catalysts. This is due to the very high throughput speed of coil coating lines where typical residence time at the PMT (Peak Metal Temperature) is 20-35 seconds.
The alkaline nature of Pigmentan grades may occasionally cause formulation instability and slow cure with the acidic catalysts. The use of blocked catalysts are therefore recommended, together with minor formulation modifications. The use of acidic ingredients such as certain organic corrosion inhibitors should be avoided.
Choice of the blocked catalyst is of critical importance for the successful performance of the formulation. They should be tested for performance, paint stability and cure retention after accelerated aging. For blocked Isocyanate systems containing Pigmentan, the use of tin based catalysts is not recommended.