Formulators Forum—What Does Superdurable Really Mean?
Posted on Thursday, September 21, 2023
A real pet peeve of mine is when, due to a lack of education, the wrong thermoset powder technology is used for a particular application and ultimately fails. In such cases, the powder coating technology itself often takes the hit as a bad choice when, in reality, if the selection process was performed correctly and the preparation and application done properly, it would have been the absolute best choice for the job.
When formulating a product, typically the first order of business is to understand the end use and environmental conditions to which the end product will be subjected. If you do not have that information available, it is important to at least understand if it will be for an indoor application or an outdoor application. This alone can help narrow down resin selection. For example, for an outdoor application, you would rule out an epoxy or an epoxy/polyester hybrid as these resin systems offer virtually no UV protection.
Keep in mind, however, that once you determine it is for an outdoor application, your work is not complete. To best serve the customer you ideally want to know not only what atmospheric condition the finished part will be subjected to, but how long it needs to last in that environment. Most in our industry are aware of the AAMA standards developed for outdoor durability specifications in aluminum applications. The better-known specifications for aluminum extrusions are AAMA 2603 for a one (1) year specification, AAMA 2604 for a five (5) year spec, and AAMA 2605, designed for ten (10) year durability.
When it comes to powder coatings, especially those developed for outdoor use, there can be some misunderstanding of terminologies, specifically as they apply to superdurable powder coatings. I think some, if not most, of the confusion is due in part to the fact that we as powder producers have made it confusing. For example, we might say superdurable powder coatings must be used to meet AAMA 2604 specifications, but we may also say not all superdurable powder coatings meet AAMA 2604 specifications. While both statements are absolutely true, they appear to contradict each other.
Let’s start with the reason superdurables were developed in the first place. The term superdurable was first used to refer to the polyester resin used to enhance the outdoor durability of the coating for UV resistance. The primary way UV durability is measured is in gloss retention and color shift. It is important to also understand that resin is not the only ingredient that impacts outdoor durability/weathering. If you move to a superdurable resin without changing to outdoor durable pigments or without evaluating the fillers and/or extenders as well as all the other components, improvement in outdoor performance may be minimal, and in some cases there may be no improvement at all. The term superdurable in and of itself is not enough to meet the AAMA 2604 specification for weatherability. Figure 1 shows three TGIC formulations and their associated gloss retention over five years. The first is a standard durable resin, the second a superdurable resin, and the third a superdurable resin, optimized filler and extenders, and high-performance pigments.
Let’s revisit the two earlier, seemingly contradictory statements about superdurables. Yes, a superdurable resin must be used to meet AAMA 2604 weathering requirements, but achieving this spec cannot be assumed for all superdurable products. The entire formulation must be reviewed and optimized for the weathering requirements and/or chemical testing required under AAMA and to match your performance requirements.
Steve Houston is vice president and business director for Vitracoat, Inc.