Technology Transfer Network - Air Toxics Web Site
Powder Wood Coatings
The newest low-VOC/HAP coating technology for wood is powder coating. Powder coatings also produce the lowest VOC/HAP emissions (little to none) because there is no solvent. The general application process involves: applying charged powder particles to the grounded, preheated substrate by electrostatic spray gun; heating the substrate to cause the particles to "cure" or melt together to form a continuous coating; and cooling the substrate. At this time, powder-coating technology is best suited for flat, engineered-wood components (e.g., medium density fiberboard [MDF]) finished with pigmented coatings.
Powder coating has been used in the metal-finishing industry for many years, but application on wood introduces several potential problems. The main difficulty encountered with applying powder coatings to wood is creating adhesion between the powder particles and the wood prior to curing. Powder coating wood products is more difficult than powder coating metal because the wood cannot be grounded as well. The adhesion of the powder particles to the wood can be improved by heating the wood prior to applying the powder. Heating equalizes the moisture across the surface, allowing electrostatic deposition.
Another difficulty with powder on wood applications is the sensitivity of the wood to high temperatures. The powder cannot be cured at the temperatures typically used when coating metals. Excess temperatures would cause deformation of the wood. However, the powders used on wood have been specially formulated for the low curing temperatures. Safety concerns include the potential for the powders to form explosive mixtures with the air.
Powder coatings produce a more consistent finish than sprayed liquid coatings because drips, runs, and bubbles are eliminated. Rework also is decreased. The finish is more durable and corrosion-resistant. Generally, only one coat is required to achieve the desired appearance.
Powder coatings also have many economic advantages over other types of low-VOC/HAP coatings. Once implemented, the coating line is automated and requires few operators. Cleaning solvents are not necessary. Any powder overspray can easily be collected and mixed with new powder for re-use. By collecting overspray, there is little to no coating waste. Any powder waste that is generated is not considered to be hazardous and can easily be disposed of. The production level is higher than that of a liquid line because only one coat is applied and the cure time is very short. Powder coating also costs less per coated area than liquid coatings. However, the technology is still very new; therefore, capital costs for researching and implementing the system are high.
Powder Coating Case Studies
E. Greenville, PA
|Office furniture||Waterborne, UV-curable, powder coatings, hot melt adhesives|
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