Powder Coating - Wikipedia

The powder coating process was invented around 1945 by Daniel Gustin and received US Patent 2538562 in 1945.[4] This process coats an object electrostatically and then cures it with heat, creating a finish harder and tougher than conventional paint. Originally used on metal manufactures, such as household appliances, aluminium extrusions, drum hardware, automobile parts, and bicycle frames, the practice of powder coating has been expanded to allow finishing of other materials.

Because powder coating does not have a liquid carrier, it can produce thicker coatings than conventional liquid coatings without running or sagging, and powder coating produces minimal appearance differences between horizontally coated surfaces and vertically coated surfaces. Further, because no carrier fluid evaporates away, the coating process emits few volatile organic compounds (VOC). Finally, several powder colors can be applied before all are cured together, allowing color blending and special bleed effects in a single layer.[5]

While it is relatively easy to apply thick coatings that cure to smooth, texture-free coating, it is not as easy to apply smooth thin films. As the film thickness is reduced, the film becomes more and more orange peeled in texture because of the particle size and glass transition temperature (Tg) of the powder.

Most powder coatings have a particle size in the range of 2 to 50 μm, a softening temperature Tg around 80 °C, and a melting temperature around 150 °C, and are cured at around 200 °C for a minimum of 10 minutes to 15 minutes (exact temperatures and times may depend on the thickness of the item being coated).[6] For such powder coatings, film build-ups of greater than 50 μm may be required to obtain an acceptably smooth film. The surface texture which is considered desirable or acceptable depends on the end product. Many manufacturers prefer to have a certain degree of orange peel since it helps to hide metal defects that have occurred during manufacture, and the resulting coating is less prone to showing fingerprints.

There are very specialized operations that apply powder coatings of less than 30 μm or with a Tg below 40 °C in order to produce smooth thin films. One variation of the dry powder coating process, the Powder Slurry process, combines the advantages of powder coatings and liquid coatings by dispersing very fine powders of 1–5 μm sized particles into water, which then allows very smooth, low-film-thickness coatings to be produced.

For small-scale jobs, "rattle can" spray paint is less expensive and complex than powder coating. At the professional scale, the capital expense and time required for a powder coat gun, booth and oven are similar to those for a spray gun system. Powder coatings do have a major advantage in that the overspray can be recycled. However, if multiple colors are being sprayed in a single spray booth, this may limit the ability to recycle the overspray.