Powder Coating is a dry finishing process created by an electric charge that causes a dry powder to fuse to the surface of the metal. This is then baked in a curing oven to achieve a smooth coating. It is usually used to create a hard finish that is tougher than conventional paint.
Powder coating does not have a liquid carrier, meaning it can produce thicker coatings than conventional liquid coatings without running or sagging. It produces minimal appearance differences between horizontally coated surfaces and vertically coated surfaces.
Powder coatings consist of several ingredients. A polymer resin creates the finish’s core. Additional elements in the coating include ingredients to help with curing, pigments to add color, and flow modifiers. These parts work together to create a colored, protective surface that performs well in many environments after curing.
Powder coating uses an electrostatic process and curing to adhere the powder to the surface. Because the parts must undergo high temperatures to set the coating, the substrate must also be heat-resistant. However, most products coated with this finish are metal and easily hold up throughout the process.
Generally, there are two types of powder coating – thermoplastic and thermoset. These differ in their curing methods and properties.
First, thermoplastic is a coating that melts and flows when heated, yet maintains the same chemical composition once it solidifies. It offers better resistance to impacts in the finished product. Plus, it does not need a curing cycle. Instead, the coating requires time and high temperatures to melt, flow evenly over the surface. Because it does not undergo curing, it can soften and remelt when subjected to high temperatures. Thermoplastic powder application requires a much thicker millage than thermoset powder coatings and often does not offer as nice of a visual appearance as compared to a thermoset.
Secondly, thermoset powder coatings go through an irreversible chemical change during curing to create a long-lasting, hardened coating. While thermoset coatings still melt and flow when heated, their structure chemically cross-links to form a different chemical composition than the base resin. Because the changes after curing are permanent, this type of coating will not remelt under intense temperatures. Plus, it provides better scratch resistance compared to thermoplastics. Thermoset powder coatings develop thinner films, which can be more visually appealing than some thermoplastic. However, when applied in thick layers, it can become brittle or crack.
The durable powder coating provides a thick surface over the part. It resists damage from impacts and scratches. Unlike paint, powder coating generally does not require touch-ups due to chipping or fading. It provides long-lasting color for applications in harsh environments.