A powder coating is a paint applied in the form of a free-flowing dry powder. Unlike traditional liquid paints, which are delivered by evaporating solvents, powder coatings are usually applied electrostatically and then cured with heat or UV light. Powders can be thermoplastic or thermosetting polymers. It is often used to produce a hard finish that is harder than traditional paints. Powder coating is mainly used for the coating of home appliances, aluminum profiles, roller hardware, automobiles, bicycles and other metals. Advances in powder coating technology such as UV-curing powder coatings allow the powder coating of plastics, composites, carbon fiber and other materials such as MDF (Medium Density Fiberboard) due to the minimal heating time and oven dwell time required to process these parts.
Characteristics of Powder Coatings
Because powder coating has no liquid carrier, it can produce thicker coatings than traditional liquid coatings without sagging or sagging, and powder coatings produce minimal difference in appearance between horizontally and vertically coated surfaces. Since no carrier fluid evaporates, very few volatile organic compounds (VOCs) are released during the coating process. Finally, several powder colors can be applied before curing them all, allowing color mixing and bleeding special effects in a single layer.
While it is relatively easy to apply thick coats that cure into smooth, texture-free coatings, applying smooth thin films is not. As the film thickness decreases, the film becomes more and more orange-peel in texture due to 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 of about 80 °C, a melting temperature of about 150 °C, and a curing time of at least 10 minutes to 15 minutes at around 200 °C (exact temperature and The time may depend on the thickness of the item being coated). For such powder coatings, a film build-up greater than 50 μm may be required to obtain an acceptably smooth film. What surface texture is considered ideal or acceptable depends on the final product. Many manufacturers prefer a level of orange peel, as it helps hide metal imperfections that occur during the manufacturing process, and the resulting coating is less prone to fingerprints.
There are very specialized operations where smooth films are produced using powder coatings of less than 30 µm or Tg below 40 °C. A 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 in size into water, then very smooth, low film thickness coatings can be obtained coating. produce.
For garage-scale jobs, small "rattle" spray painting is less expensive and less complicated than powder coating. On a professional scale, the capital outlay and time required for powder coating guns, spray booths and ovens is similar to Spray Gun systems. The main advantage of powder coatings is the ability to recover overspray. However, this can limit the ability to reclaim overspray if multiple colors are being sprayed in a single paint booth.
Advantages over other coating processes
Powder coatings contain no solvents and release little or no volatile organic compounds (VOCs) into the atmosphere. As a result, finishers do not need to purchase expensive pollution control equipment. Companies can more easily and cost-effectively comply with environmental regulations, such as those issued by the U.S. Environmental Protection Agency.
Powder coatings can produce thicker coatings than traditional liquid coatings without sagging or sagging.
The difference in appearance of powder-coated items between horizontal and vertical coated surfaces is generally less than that of liquid-coated items.
Various special effects can be easily achieved using powder coatings, which cannot be achieved by other coating processes.
Powder coatings have significantly faster cure times compared to liquid coatings, especially when using UV curable powder coatings or excellent low bake thermosetting powders.
