Thermoplastic Coating Basics
Thermoplastic coatings are similar to powdercoating in that they can also be applied with an electrostatically charged powder, amongst other techniques. They are also quite different, due to the fact that thermoplastic coatings do not ‘set’ when heated, and can therefore be repaired with heat.
Many forms of plastic can be applied as a decorative or protective coating on metal parts. Generally there are three basic methods of application.
Fluidised bed application, where pre-heated parts are immersed in a bath of air-fluidised plastic powder. The heat from the metal part melts the plastic powder and coats the metal’s surface.
Spray application, where the preheated part is sprayed with the plastic powder and the retained heat melts the plastic powder.
Electrostatic Spray application, where the part is treated much like conventional powdercoating. A powder is sprayed through a special gun which charges the powder for electrostatic attraction. The dry film on the components is then heated to melt and flow. Note that not all plastics are suitable for this application method.
These coatings are generally thicker than conventional powdercoating finishes, with a thicknesses in excess of 200 microns not being uncommon.
Although most of these plastic materials can me made in any colour, stock lines are rather limited.
Plastic coatings can range from a common PVC, polyethylene and nylon to much more complex engineering formulations. There are a number of special formulations available that give improved adhesion, UV exposure or other specialised properties.
Typical applications for plastic coatings would be the ever-present supermarket shopping trolley, which is a great demonstration of the use of this tough coating. The trolley’s chemical, UV and impact resistance are all key properties possessed by thermoplastic materials.
Like most coatings, the preparation of the metal before coating is very important. This may range from abrasive blasting to special primers.