Uses of powder coating
From the shelf grills in refrigerators to the handrail on the office stairs, powder coating is used in thousands of applications to give products more visual appeal, a more pleasant tactile experience, and sometimes different properties in terms of electrical and heat conductivity.
We are so used to seeing powder-coated metals that they go largely unnoticed, but they are not all the same. There are different types of coating available, each having different properties. One of the more common is Thermoset Powder Coating, but what is it, how does it work, and what can it do?
Powder Coating Process
The powder coating process has established itself since its inception in the late 1940s and involved spraying the powder onto an item using an electrostatic spray gun, charging the powder and causing it to be attracted to the item in a thin layer. With the item heated beyond the melting point of the powder prior to application the powder melts and adheres to the surface as a thin, paint-like layer.
Today, we can also use a fluidized bed application process, as pioneered by German scientist Dr Erwin Gemmer. Here the item is heated beyond the melting point of the powder, but instead of powder being applied to the object, the object is then dipped into the powder, melting and bonding the powder as a result.
It is during this process that thermoset powders show why they are so useful. As the powder heats and melts, it flows around the surface of the object being coated, and undergoes a chemical change called cross-linking, which forms a tough, solid surface that protects the object being coated.
It is this process, with the chemical change, that make thermoset powder an effective coating for all kinds of objects, providing a number of protective qualities as well as visual appeal. The exact nature of the protection depends on the type of thermoset powder being used, with different formula being chosen depending on the requirements for the coating project.
There are several types of thermoset powder, derived from epoxies, acrylics, hydroxyls (polyester) and carboxyl (polyurethane) groups, although the most common are epoxy and polyester based options. Epoxy resin based thermoset powders form a tough impact resistant coating that has excellent corrosion resistance, however they also tend to display poor UV resistance, so are most frequently used for internal applications as the color and gloss finish tend to degrade quite quickly when exposed to direct sunlight.
Polyester-based coatings share the same tough performance once cured, but are highly UV resistant, making them an ideal choice for outdoor applications. Other forms of thermoset powder have a variety of performance capabilities that are used for specific situations.
Acrylic-based thermoset powders form a beautiful, thin glossy coating that has excellent UV resistance, and offer good chemical and corrosion resistance too, but are less hard wearing than other options. Great for outdoor use, but not in areas where they would attract a lot of wear, such as handrails and similar.
For thermoset powders based around polyurethane resin, they produce excellent, hard-wearing coatings with high gloss resilience, and present a versatile option that performs well in most applications.
Getting the best performance from any powder coating requires choosing the right materials, and thermoset coatings are no different in this regard.
The benefits of thermoset powder coating
One of the key aspects of thermoset powder coating is the chemical change that takes place during the process. This is not present in other options such as thermoplastic powder coating and is the reason why thermoset coatings are so hard wearing. In its powdered state, thermoset material or any type tends to have a much lower molecular weight that other coating materials, usually requiring less heat to melt, making it a more energy efficient process.
The cross-linking that occurs, whether between molecules of the coating itself or with other reactive elements, forming a coating with a much higher molecular weight, and it is here that the advantages materialize.
The resultant finish is robust, and can be created in gloss or semi-gloss, making it ideal for a wide variety of applications, with everything from home appliances such as refrigerators and washing machines to garden furniture and a wide range of marine and industrial equipment depending on the exact thermoset powder being used.
Next time you see a large truck pass by, take a look at the wheels, possibly one of the harshest environments for everyday use, they are exposed to the weather, road salt and all kinds of contaminants every day. Polyester-based thermoset powders are frequently used to color and protect these wheels, with the extremely hard-wearing nature of the finish and array of colors providing excellent properties for this application.
Polyurethane based coatings offer some of the highest levels of weather resistance, and as such are often used in light poles and building facades, as well as industrial applications where objects will be exposed to corrosive environments, including sea water and chemical spills.
Appearance of thermoset coatings
While the overall properties of the thermoset powder coating provide a range of options to suit most situations, it is the appearance of the cured coating that we notice most. In the early days of the technology, there were few options, but today, no matter which type of thermoset powder coating chosen, there is an almost limitless range of colors and finishes available.
Bespoke color mixes are possible, but with thousands of shades available off the shelf there is usually something to suit any project. But the possibilities do not end with the color choice, everything from completely matte to a high gloss finish are also available, alongside a range of tints that add a metallic look, hammertones that give an antique look, a weathered look, and granite or marble effects, even a rusty appearance is possible if needed. This combination of high performance and almost endless appearance options means there is a thermoset powder coating option for almost every application. We interact with them every day,