Coil coating processes are characterized by a very high throughput speed and very short time between application and the curing zone. 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 (Pick Metal Temperature) is 20-35 seconds.
The alkaline nature of Pigmentan grades may cause stability and loss of cure problems with the acidic catalysts, and therefore blocked catalysts are frequently used and slight formulation adaptations are needed. In view of this, acidic ingredients like some organic corrosion inhibitors should not be used.
Pigmentan Ltd. developed a special grade for coil coating primer applications -Pigmentan CC which proved to excel common non chrome anti corrosion pigments like Ca-Ion Exchanged Silica. The suggested loading of this product is 3.5- 5.5% by weight on the total formulation but it is recommended to further optimize it for the specific substrate. Super fine product is also available for 5 micron DFT primers.
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 non tin catalysts are recommended.