Powder coatings are divided into thermoplastics and thermosets. Thermoplastic powders melt and flow into a smooth sheet that hardens upon cooling, while thermosetting powders undergo a chemical change during the curing process. Both types provide a durable and attractive finish and are used as an alternative to wet paint application. Thermoplastic powders are used in interior and exterior applications, while thermosetting powders are ideal for higher temperature environments. Powder coating is created by mixing granules with hardeners and pigments, heating, extruding, crushing, and grinding. The powder itself does not have adhesion properties and requires the work piece to be primed or electrostatically charged. Powder coating is often used as an alternative to metal plating and results in a lustrous, hard, and durable surface.
The different types of powder coatings can be divided into two broad categories: thermoplastics and thermosets. Thermoplastic powders are applied to the work surface and heated, or hardened, during which they melt and flow into a smooth sheet that hardens upon cooling. Thermosetting powders work in much the same way, except that the curing process alters their chemical structure. Both types are used as an alternative to wet paint application, particularly for items such as appliances, automobiles and motorcycles, and both provide a durable and attractive finish. Additionally, both types of powder coatings are used as coatings for metal objects that are not visible but need protection from corrosion and oxidation.
Thermoplastic powder coating powder includes substances such as nylon, polyvinyl chloride (PVC), polyolefin and polyester. Each melts at different temperatures, and upon re-exposure to that temperature, will melt again. This makes recycling easier, but limits the use of thermoplastic powders to environments where the temperature is unlikely to reach melting point. These coatings are typically used in interior and exterior applications, such as appliances, automotive surfaces, and patio furniture. Furthermore, most of these substances have special properties which make them particularly suitable for certain applications. Nylon, for example, is often used as a coating on gears and conveyor components due to its low coefficient of friction. Polyester, on the other hand, is abrasion resistant, looks good, and holds up well to the elements, making it ideal for outdoor furniture and exposed car parts.
Thermosetting powder coating, once melted into a smooth finish on a workpiece, does not melt upon re-exposure to the original melting temperature because the chemical change it undergoes, called cross-linking, chemically bonds the separate components together during the casting process. polymerization to create new compounds. In addition to having greater heat resistance than thermoplastic powders, they are also generally harder. Some of the different thermoset materials are epoxies, acrylics, epoxy polyester hybrids, and silicon-based powders. Their heat resistance makes them ideal for higher temperature environments such as automotive components of exhaust systems, oven interior walls, and oven and barbecue grills. Some, like epoxy resin, react poorly to ultraviolet (UV) rays, found in sunlight, limiting their usefulness to environments where they won’t be exposed to the sun, such as underground pipelines.
Powder coating powder is created with a basic process: the granules are mixed together with hardeners and pigments, heated and extruded into a sheet, which is then crushed into chips which are then ground into a fine powder. Unlike wet paint, which requires a solvent in which the paint particles are suspended, dry powder coating is dry when applied. Some of the powders are sprayed onto the surfaces to be painted, while others are placed in a bath in which the work piece is immersed. The powder itself does not have adhesion properties, requiring the work piece to be primed or electrostatically charged for the powder to adhere to the surface prior to the heating or curing process.
Powder coating is often used as an acceptable alternative to metal plating. Interestingly, while metal plating deposits an extremely thin layer of metal on a work piece, sometimes only thousandths of an inch thick, powder coating an object will result in a lustrous, hard, and durable surface. sometimes up to a quarter inch to one half inch thick (0.635cm – 1.27cm). In fact, the thicker the powder coating, the smoother it will feel on the painted object; very thin coatings tend to be pebbly in texture rather than smooth. Electroplated coatings, on the other hand, will be very smooth no matter how thin they are applied, as long as the piece itself has been sanded and smoothed.
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