Powder coating
Powder coating is a type of coating that is applied as a free-flowing, dry powder. The main difference between a conventional liquid paint and a powder coating is that the powder coating does not require a solvent to keep the binder and filler parts in a liquid suspension form. The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a "skin." The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals, such as "whiteware", aluminium extrusions, ceramic coatings and automobile and bicycle parts. Newer technologies allow other materials, such as MDF (medium-density fibreboard), to be powder coated using different methods.
There are two main categories of powder coatings: Thermosets and thermoplastics. The thermosetting variety incorporates a cross-linker into the formulation. When the powder is baked, it reacts with other chemical groups in the powder polymer and increases the molecular weight and improves the performance properties. The thermoplastic variety does not undergo any additional reactions during the baking process, but rather only flows out into the final coating.
The most common polymers used are polyester, epoxy powder coating polyester-epoxy (known as hybrid), straight epoxy (Fusion bonded epoxy) and acrylics.
Production:
The polymer granules are mixed with hardener, pigments and other powder ingredients in a mixer
The mixture is heated in an extruder
The extruded mixture is rolled flat, cooled and broken into small chips
The chips are milled to make a fine powder
