Powder Coating Non-Conductive Substrates

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.

Today’s low cure powder

Low cure technology is now designed to overcome all of these hurdles. The newest powder offerings such as IFS PureClad Powder, and improved application and cure systems, mean coaters now have access to an efficient, effective operational system that is suitable to coaters of all sizes and capacity requirements. A coater doing a few cabinets a week and an OEM manufacturing thousands of cabinets a week can coat efficiently and cost-effectively. Both the coater and their end-use customers will also enjoy the benefits of a powder coated surface, including improved technical performance and a better environmental footprint.  

In looking at IFS PureClad Powder as an example, the goal was to achieve full cure, without compromising aesthetics or performance, and at temperatures sufficiently low to avoid damaging heat-sensitive materials. From a practical perspective, we also had to mitigate the effects of moisture content, which affects deposition during electrostatic application and can result in outgassing during cure.

Another technical hurdle centered on uniformly applying powder to non-conductive or minimally conductive substrates; as well as materials on which conductivity can vary considerably across the surface of the substrate. Likewise, the tendency for wood-based materials to shrink and swell over the life of finished products as they absorb and release moisture means the coating has to be sufficiently flexible to accommodate this tendency without cracking or peeling.

Finally, to make it a viable prospect, we also wanted to ensure a cost-effective solution with an optimized operational footprint was available for coaters of all sizes.

The resulting product, PureClad, cures at around 265°F in a catalytic IR oven for only a few minutes, which overcomes the issue of damage to the substrate. The powder also has the flexibility to adapt to the shrinking/swelling issues these substrates display, applies in a very smooth uniform finish and is not prone to outgassing like some of its predecessors. We have also partnered with application and curing experts to offer cost-effective systems with an economical footprint to make applying the powder a truly viable option. What’s more, these new systems mean that both wood and metal parts can be cured in the system — an attractive proposition, especially for smaller coaters coating many different types of jobs.