POWDER COATING GUIDE
Information provided by the Powder Coating Institute and the Powder Coating Finisher's Handbook. Additional information regarding powder coating can be found on their website at www.powdercoating.org .
Powder coatings are supplied ready for immediate use without additional pre-mixing, stirring, solvent additions, or viscosity adjustments. Besides the obvious savings in labor, finish quality variations are minimized. Even before the days when regulation mandated the use of low-VOC coatings, liquid paint users encountered problems such as pigment setting, poor atomization due to high viscosity, or sagging due to over-reduction with solvent. With waterborne or high solids coatings, the goal of consistent applied finish quality frequently becomes even more difficult to achieve. With powder, the absence of extra mixing means less process variation and better control over finish quality.
A major quality advantage with powder coated parts is the ability to achieve the optimum film thickness in a single pass without problems of drips, sags, or runs. The definition of what constitutes the optimum film thickness varies considerably with the design of the part as well as its intended end use. Powder coatings currently are being applied in film thickness exceeding 15 mils (375 microns) for applications requiring high dielectric strength or especially good corrosion resistance.
At the other extreme, powder can also be applied in thin films of less than 1.0 mil (25 microns) for those applications where lower film build is advantageous. At this time, the major percentage of powder applications target film thickness in the range of 1.5 to 2.5 mils (38 to 63 microns).
Powders can be formulated to provide a wide range of melt viscosities and can be applied over a wide range of film thickness. Therefore, powder can provide better edge coverage protection than can be achieved in single-coat liquid coating applications.
The general purpose powder coating formulations that are widely used have a long established reputation for providing an excellent balance of mechanical properties such as impact resistance, hardness, and abrasion resistance. Films having extra hardness, greater chemical resistance, improved exterior gloss retention, and superior flexibility are all attainable (although not, necessarily, simultaneously in a single formulation). A powder coating material can be formulated to match virtually any requirement that can be achieved by a liquid coating. However, some film property specifications, which are readily attainable with powder, are difficult or impossible to achieve with liquid paints.
The combination of proper metal pretreatment and powder coatings can provide outstanding corrosion resistance. Part of the reputation that powder has achieved for good corrosion resistance is related to powder’s ability to consistently deliver high film builds and good edge coverage. However, equally important are the facts that powders provide high crosslink density, good resistance, to hydrolysis, low moisture and oxygen transmission rates, and films free from traces of any residual solvents.