By Kevin Biller, ChemQuest Powder Coating Research
The past year marked a rebound in powder coating revenue as well as investment in R&D. In particular, both the North American and Latin American powder markets showed growth of 3.5% and 1.8%, respectively, in 2022.1 These growth figures coincided with the introduction of several innovations in sustainability, low-temperature cure, corrosion resistance, outdoor durability, thin films, and thermoplastic application technology.
Sustainability
Sherwin-Williams recently introduced a powder coating product line based on post-consumer recycled plastic. Powdura® ECO powder coatings are formulated with polyester resins based on recycled polyethylene terephthalate plastic (rPET). Earlier versions of Powdura® ECO powder coatings were based on pre-consumer waste plastic that is generated in factories. This latest development will have an impact on recycling post-consumer plastic that comes mainly from beverage bottles.
According to the company, one pound of Powdura ECO TGIC/TGIC-free (triglycidyl isocyanurate) coatings contains the rPET equivalent of about sixteen 16-ounce water bottles, depending on the final product formulation Sherwin-Williams estimates that one pound of Powdura ECO hybrid coatings contains approximately the rPET of seven to ten 16-ounce water bottles, depending on the formulation.
Low-Temperature Cure
Pengchen (Simon) Yang, a senior researcher in allnex’s Corporate Innovation Group located in Wageningen, Netherlands, introduced a potentially game-changing powder technology at the 2023 European Coatings Conference. The breakthrough was described in his presentation, “Ultra Low Temperature Curing Powder Coating via Real Michael Addition.”
Yang’s work introduces a new chemistry to the low-temperature-cure powder coating universe. This fascinating technology is based on Real Michael Addition (RMA) chemistry that includes an innovative catalysis system that provides cure latency to this highly reactive chemistry. An RMA reaction relies on a combination of a “Michael donor” in the form of a nucleophile with an α,β-unsaturated carbonyl to create a Michael adduct. The allnex team, led by Yang, crafted this chemistry into solid polymers/oligomers that are extrudable and capable of film formation at relatively low temperatures, i.e., < 120 °C. In addition, these polymers/oligomers are reportedly stable at room temperature storage conditions.
This chemistry is comprised of two crosslinkable species: component A is a material containing C-H acidic moieties, and component B is an unsaturated polymer. The most preferred component A is a malonate functional polyester resin, and methacrylated polymers (polyester-, epoxy-, or urethane-based) are the most preferred B component.
The catalysis system is rather complex and is based on a catalyst precursor (P1) in combination with a catalyst activator (C1). P1 is a weak base (DABCO™ or tetramethyl guanidine) that reacts with C1, generally an epoxide compound, to produce a strong base catalyst. The epoxide compound can be TGIC, glycidyl methacrylate (GMA) acrylic resin, or Araldite™ PT-910/912. This catalyst technology is quite reactive; therefore, a retarder, typically a carboxylate, is used to introduce a degree of latency. Latency is critical to enable processing through the conventional extrusion techniques that are common in the powder coating industry.
Latency is further enhanced by macro-physically separating reactive species in independent compounded mixtures. For example, the C1 catalyst activator may be extruded into binder components independent of the P1 catalyst precursor/retarder blend. Two powder materials are generated that are then post-blended into a pseudo-2K powder mixture that is then applied to a substrate and cured at low temperatures, typically about 110–130 °C.
This groundbreaking technology is comprehensively detailed in the international patent application WO-2022/236519 A1, which was issued on November 17, 2022. It is the author’s hope that the powder coating world will take notice of Yang’s fascinating low-temperature RMA-curing technology and that this will open a spectrum of opportunities for growth into new markets and applications.
In other developments, AkzoNobel debuted Interpon W, a product group specially formulated for application to heat-sensitive substrates. Not only can these products be used to coat wood and engineered boards, but they can also be used on various plastics, gypsum, and plastic composites. Interpon W includes thermoset as well as UV-curable powder technologies. Allnex Resins is also supporting the development of low-temperature-cure powder coatings with the introduction of ultra-low-temperature-cure polyester resins. These include UVECOAT (UV cure) and Crylcoat (thermoset) resins specifically designed to cure at temperatures 80–135 °C.
Continue reading in the July-August digital issue of CoatingsTech.