Q: While doing some research on thermoplastic powder coating, an idea came to my mind. I don’t know if anyone has tried this out or if it’s nonsense. One of the benefits of thermoplastic powders is that they eliminate or reduce coating porosity. This is often a problem, especially on galvanized steel. We tend to apply the epoxy primer after preheating the metal structures to avoid pinholes.
Would it be commercially viable to apply the primer as thermoplastic in a fluidized bed and then apply the top coat with a gun? Also, I saw other methods such as flame spraying powder, like the metallizing method of applying zinc wire. I would appreciate your advice on this.
A: This is definitely something to explore. As you know, thermoplastics do not chemically react to form a tight, three-dimensional molecular network. Hence, they can reflow (move) when heat is reapplied. This may cause wrinkling of a subsequently applied coating, such as a topcoat.
Thermoplastic powders include a vast array of polymer types with varying molecular weight and rheological performance (melt point and viscosity). As a result, some are rather soft like PVC or hard like polyamide (nylon).
Examples of thermoplastic polymers used as powder coatings include PVC, nylon, polyethylene (high density and low density), polyester, copolymer, PVDF, and PTFE. The copolymer types are evolving, and some now offer the toughness of a soft, elastic polymer with a harder, more rigid one that provides improved hardness and scratch resistance.
Nevertheless, I would investigate commercially available thermoplastic powder coatings that are described as primers. In particular, I would check out the polyamide powders on the market. This could be a great idea. Please keep in mind that thermoplastics are typically applied at relatively high film builds, commonly 150-200 microns depending on the type and particle size.
Another thing – many thermoplastic powder coatings are offered in “electrostatic spray grades” so fluidized bed application or ES spray could be contemplated. As for flame spray – I’m not a big fan. It takes specialized equipment and film thickness control would be an issue. Furthermore, I don’t like the idea of introducing a cloud of combustible organic particles into a source of ignition.