Q: We know powder coating is electrostatically applied and then cures in an oven — what’s changed that we can now put powder coatings on a non-conductive substrate like wood or MDF (medium-density fiber board) then cure it in an oven without affecting the substrate?
A.Today’s low cure powders, such as IFS PureClad powders, targeted at non-conductive substrates have benefitted from a huge amount of R&D investment, technical expertise and essentially cure very quickly at very low temperatures. What’s more, advances in application and cure technology — for example, the global success of catalytic IR oven technology — mean that combined with these low cure powders, finishers now have an extremely effective operational option for finishing non-conductive substrates like wood and MDF.
Much work has been done on formulations for wood and MDF, but other substrates such as fiberglass, drywall and many others are also viable options.
A variety of applications
Manufacturers of kitchen cabinetry, commercial casework, hospitality furniture, pre-finished sheet goods and office furniture manufacturers are extremely excited about the potential these low cure powder coatings can deliver. Improved technical performance and environmental footprint tick the functionality and environmental boxes that designers and manufacturers are looking for.
Learning from the past
Powder coatings for wood have been tried in the past, with limited results. Fortunately, we have learned from past challenges. The first real attempts began in the 1990s with the launch of a UV-cured acrylated polyester system, but drawbacks such as the lack of coating flexibility to accommodate the swell/shrink tendency of wood/MDF meant limited uptake.
This was followed up in the mid-1990s with UV-cured unsaturated polyester-urethane powders. These products provided the flexibility needed to accommodate this shrink/swell tendency, however, there were drawbacks due to the curing system. For example, UV light won’t cure what it does not “see,” thus limiting the type of shapes that can be coated. UV curing also limits the colors available. In addition, UV cure results in very high crosslink densities, which can yield poor inter-coat adhesion.
In the late 1990s-early 2000s, thermoset powders made it onto the heat-sensitive substrates stage and progress was made, especially in the MDF office furniture segment. Thermoset powders, which do not require UV cure, could be applied in thick film layers, re-coated, and could produce relatively smooth finishes with good edge coverage. However, there were still challenges. For example, if moisture was present, defects due to outgassing would often occur. Consequently, the application and cure process involved 15-20 minutes of pre-heating in a conventional oven, to achieve a substrate temperature of about 300°F and a very dry board. This meant more expensive grades of MDF had to be used — the “standard” MDF was not suitable. In addition, this application system required high-energy consumption and a large space requirement.