Powder Curing

Thermoplastic powders require heat only to fuse the powder together into a continuous film. However, thermosetting powders often require additional heat to cure the film on the product. There are four basic methods normally used in the curing of powder coated parts: convection, infrared, a combination of the two, and ultraviolet (UV) curing.

Convection ovens can be either gas or electric. Hot air is circulated around the powder coated parts, and the parts attain the temperature within the oven. UV curing is commonly used with heat sensitive substrates. Specifically formulated UV powders flow at very low temperatures (121°C) and can be cured via UV radiation in a matter of seconds.

Infrared ovens, using either gas or electricity as their energy source, emit radiation in the IR wavelength. The radiated energy is absorbed by the powder and the substrate immediately below the powder, so the entire part need not be heated to the cure temperature. This allows a relatively rapid heat rise causing the powder to flow and cure when exposed for a sufficient time. Combination ovens generally use IR as the first zone to melt the powder quickly. This process is termed near infrared (NIR) cure, and powders are formulated specifically to take advantage of this process. The part then progresses into a second zone, which is a convection oven.

Table 1 provides a comparison of general curing conditions for heat curing of conventional thermosetting powders and UV curable powders using the various heating modes described above.