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 ususally used to create a hard finish that is tougher than conventional paint. Powder coating is mainly used for coating of metals,such as household appliances, aluminium extrusions, drum hardware and automobile and bicycle parts. Newer technologies allow other materials, such as MDF(medium-density fibreboard), to be powder coating using different methods. The powder coating process was invented around 1945 by Daniel Gustin US Patent 2538562
Properties of powder coating
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 apprearance difference between horizontally coated surfaces and vertically coated surfaces. Because no carrier fluid evaporates away, the coating process emits few volatile organic compounds. Finally, several powder colors can be applied before curing them all together, allowing colors blending and bleed special effects in a single layer.
While it is relatively easy to appy thick coating which 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 dur to the particle size and glass transition temperature of the powder.
Most powder coatings have a particle size in the range of 2 to 50, a softening temperature around 8 c, a melting temperature around 150, and are cured at around 200. for 10 minutes to 15 minutes(exact temperatures and times may depend on the thickness of the item being coated. For such powder coatings, film build-ups of greater than 50 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 actually prefer to have a certain degree of orange peel since it helps to hide metal defects that have occurred during manufactur, and the resulting coating is less prone to showing fingerprint/
Advantages of powder coating instead of other coatings
- Powder coatings contain no solvents and release little or no amount of Volatile Organic Compounds (VOC) into the atmosphere. Thus, there is no longer a need for finishers to buy costly pollution control equipment. Companies can comply more easily and economically with the regulations of the U.S. Environmental Protection Agency.
- Powder coatings can produce much thicker coatings than conventional liquid coatings without running or sagging.
- Powder coated items generally have fewer appearance differences between horizontally coated surfaces and vertically coated surfaces than liquid coated items.
- The wide range of speciality effects are easily accomplished using powder coatings that would be impossible to achieve with other coating processes.
- Curing time is significantly faster with powder coating as compared to liquid coating