Coating laboratories can spend immense time and resources screening various additives to remedy defects on cured surface coatings. However, in some cases, the powder coating processing from extrusion to spray application may be the cause of significant changes in defects for powder coating systems, resulting in early film failure. We compared various preparation methods to changes in surface appearance and physical performance for various exterior topcoat powder systems over metallic substrates. This study will utilize accelerated corrosion testing to evaluate how a powder system's preparation can affect the topcoat's overall performance in exterior weathering.
Fluoroethylene vinyl ether (FEVE) resins were developed to overcome some of the challenges of traditional fluoropolymer resins exhibited in paint coatings. FEVE resins are synthesized from two monomers, fluoroethylene, and vinyl ether. When these monomers undergo radical polymerization, they produce amorphous A-B-type polymers shown below (Figure 1).
These high-performance polymers create a strong polymer resin with an excellent collection of physical and chemical properties. FEVE resins contain functional hydroxyl groups, allowing the resin to crosslink with standard aliphatic isocyanates. In addition, the incorporation of vinyl ether groups into the polymer provides solubility, making it an incredibly easy material for paint formulations. Typical properties of FEVE resins are shown in Table 1.
The fluoroethylene groups provide remarkable strength to FEVE resins in terms of UV light exposure. Traditionally, total fluorine content is used as an indicator of overall UV performance. But with FEVE resins, the fluoroethylene units alternate with the vinyl ether groups, creating steric hindrance and chemical protection for the neighboring vinyl ether units. FEVE resin's incredible performance against the sun's UV radiation makes them an excellent material for long-term exterior weathering. Paint coatings formulated with FEVE resins endure harsh exterior weathering with minimal loss of appearance and performance. FEVE coatings are used to protect bridges and other large structures for decades. Multiple case studies have been reviewed, and it has been observed that FEVE-based topcoats also protect the underlying coatings from corrosion. Overall gloss retention results in brilliant color retention and a fresh appearance over the years (Figure 2)1,2.
