Q: I’m looking for a degassing agent for a low-temperature-cure powder coating. What are your recommendations?
A: We may need more information to fully answer your query. Degassing agents can be used for a variety of phenomena:
- Some “gassing” is related to the expulsion of interstitial air between powder particles as they fuse and form a film.
- Some cure chemistries emit volatiles, including e-cap blocked polyurethanes, glycoluril crosslinked polyesters, and hydroxyl-alkyl amide (e.g. Primid®) cured polyesters.
- A small amount of moisture (< 0.5%) is normally present in powders. Degassing agents are essential in all these scenarios.
Another gassing phenomenon involves the expulsion of gases (air, water vapor, and even hydrogen) that are associated with substrates like cast metals, galvanizing, etc. This is commonly referred to as “off-gassing” or “outgassing.” A different set of degassing agents works for these phenomena.
Formulating for degassing is tricky business. Benzoin works very well for gas release in standard-bake powder coatings. This pertains to the air, moisture, and cure chemistry volatiles degasification phenomena. It doesn’t work so well in low bake (< 130°C bake powders) because its melt point is around 132°C and it is rendered ineffective below that temperature. Hence, you need to consider more specialized proprietary products from additives suppliers.
As for “off-gassing” or “outgassing,” the secret sauce is based on a wax. These waxes allow the coating to stay soft and “open” during the melt and cure cycle. This open phase allows the volatiles from the substrate to evolve through the coating. After volatiles have exited the coating, the wax reflows to fill the void created by the evolution.