Q: What can you tell me about VOCs in cured powder coatings? I know there is a very negligible amount, if any, during the curing process, but I cannot find any literature online about the matter.
As I am young and new to the coating process, I am told that there is not enough concentration to worry about, but the end customer wants literature about the matter to further interest him in the powder coating process.
A: The VOC issue is somewhat complicated. The initial ASTM test method was run at 105°C for 60 min and produced essentially zero VOCs with any powder coating. A little moisture would be emitted but nothing else.
The most current technique appears to be ASTM D2369, which is run at 110°C for 60 min. In this case, as in many cases in life, the real answer and the “official” answer may not jibe. Powder coatings can have volatiles of cure, and these volatiles may or may not be considered VOCs. Here is a brief rundown of the VOC picture for powder coatings:
Essentially no volatiles of cure
- Epoxies
- Hybrids
- Polyester TGIC
- Polyester GMA acrylic
- Polyester urethane (uretdione)
Benign volatiles of cure
- Polyester HAA (water)
- Polyester TMMGU (methanol)
- Polyester urethane (e-caprolactam)
Not-so-benign volatiles of cure
- Polyester urethane (MEK Oxime)
- Polyester urethane (Pyrrole)
In addition, other volatiles unrelated to the cure chemistry are emitted into the environment during the powder baking process:
- Benzoin
- Water
- Low-molecular-weight monomers and oligomers
- Some waxes
- Some antioxidants
- Some HALS and UVAs
- Miscellaneous organic additives
How you handle your customer requires careful research of your product(s), the customer process, local regulations, and their culture. I would suggest that you evaluate your products in question using ASTM D2369 and also the recommended cure conditions. You can simply gravimetrically determine the non-volatile content at these conditions to provide knowledge of amount of material emitted.
You also can have an analytical lab perform a head-space analysis of volatile components using FTIR and GC-MS (gas chromatograph – mass spectroscopy). This will give you a fairly precise readout of what’s coming off your product. How you report your findings to your customer is a judgment call.