Formulators Forum—Developing Resins to Meet New Demands
Posted on Friday, January 21, 2022
Most of us only see powder coatings in their final, usable state. But manufacturing powder coatings is a precise process where raw materials and other ingredients are extruded, mixed together in specific amounts, and micronized to achieve a free-flowing electrostatic powder with specific appearance characteristics and chemical and mechanical resistances for finished products.
This column aims to remove some of the mystery behind where powder coating raw materials originate, what roles raw materials play in formulation, outline the powder coating manufacturing process, and introduce new technologies that are currently under research to make powder coating an even Stronger, Greener, Better finishing choice.
With the increased awareness of reducing carbon emissions and rising energy costs we have all seen in recent years, there has been a spike in the growth of electric vehicles (EVs) in the market. The transition to EVs has demanded lighter designs in almost every mode of transportation, not just cars. Less weight translates to less energy required to transport.
Truck, train, plane, jet ski, and snowmobile designs are all incorporating non-metallic composites. Carbon fiber is probably the most significant example of a composite material that can reduce a vehicle’s overall weight while striving to maintain strength and integrity.
Powder coating non-metallic substrates presents a few challenges. Composite materials often exhibit lower, or zero, conductivity, which is a critical requirement for good transfer efficiency when applying powder. Non-metallic substrates also tend to have less tolerance of typical cure oven temperatures than metal.
Collaborative efforts between composite material producers, polymer suppliers, and powder coating manufacturers will likely be needed to bring improved solutions to the market. The resin chemistries used for these types of powder coatings will continue to require lower temperature cure capabilities.
The use of polymer alloys is one potential solution to achieve lower temperature cure capabilities while obtaining unique performance properties in the powder coating formula. A polymer alloy is simply the combination of two distinctly different types of resin. A conventional hybrid powder coating used in today’s market is an example of a polymer alloy. Hybrids typically require an epoxy resin processed with either a polyester or in some cases, an acrylic resin. If we look beyond a typical hybrid powder coating, there are a variety of other polymer combinations that can result in beneficial coating performance properties. The practice of combining thermoplastic polymers, which do not require a crosslinker, with thermosetting polymers, which do necessitate the use of a crosslinker, may allow for properties not achieved when applied independently of one another.
Enhanced exterior durability of powder coatings will continue to be an area of interest for new development opportunities to the EV market as well as other applications. Fluoropolymers and superdurable polyester chemistries represent the primary resins employed in today’s powder coating market when exterior durability is required. There is a significant cost versus performance gap between fluoropolymers being the most expensive option and superdurable polyesters for high durability markets. An opportunity exists to develop a new class of powder coating with a performance range between these two types that could broaden the current offerings. Siliconized polyesters, a resin chemistry used in liquid coatings, is an example that may have increased potential in powder coatings.
Acrylic resin chemistry is also known to have excellent exterior weathering properties. One of the primary reasons that acrylic resins currently represent a smaller segment of the powder coating market is they tend to be less flexible. As a result, they are used in applications that do not require much, if any, flexibility. The challenge for resin manufacturers, as well as powder coating formulators, is to improve on those properties to perform comparably to more typical powder coating applications. Higher formulation costs of acrylics compared to polyester resin-based formulas, and minimal compatibility with other classes of powder coatings, is another challenge to overcome for future R&D initiatives.
Paul West is director of marketing at Sun Polymers International INC.