Three primary resins used in thermoplastic powder coatings
There are three primary resins used in thermoplastic powder coating, vinyls, nylons and polyesters. These materials are used for some food contact applications, playground equipment, shopping carts, hospital shelving and other applications.
Few of the thermoplastics have the broad range of appearance properties, performance properties and stability that are required in applications that use thermoset powders.
Thermoplastic powders are typically high molecular weight materials that require high temperature to melt and flow. They are commonly applied by fluidized bed application and the parts are both pre-heated and post-heated.
Most of the thermoplastic powder coatings have marginal adhesion properties so that the substrate must be blasted and primed prior to application.
Thermoplastic powders are permanently fusible. This means that, once heated, they can always be reheated and recycled into different shapes as a user desires. By contrast, thermoset powders, once heated and molded into specific shapes, cannot be reheated without charring or breaking down. The chemical explanation for this behavior is that molecules in thermoplastics are weakly attracted to each other whereas in a thermoset they are chain linked.
Van der Waals forces attract and hold molecules together. Since thermoplastics are described by weak van der Waals forces, the molecular chains that makes up thermoplastics enable them to expand and be flexible. On the other hand, once thermosetting powders are heated, they chemically react, and the new compound formed is characterized by strong van der Waals forces. Instead of forming long chains, they form molecules that are crystalline in nature, making the product difficult to recycle or re-melt once it has been cured.