The objective of this project is to demonstrate environmentally friendly polysiloxane topcoats on the exterior surface of U.S. Navy ships and submarines, then validate their performance compared to MILSpec. qualified topcoats that contain hazardous Oxsol-100 solvent and isocyanate-based molecules. Oxsol 100 is a popular solvent for use in military and commercial coatings as it does not degrade ozone and is considered an exempt solvent by the Environmental Protection Agency (EPA). It is also the only volatile organic compounds (VOC) exempt solvent with a flash point >100 °F. However, it was recently discovered to be a potential carcinogen. Additionally, isocyanates can result in environmental and health issues during normal painting applications such as touch up and repair. The new polysiloxane topcoat formulations, which will be Oxsol-free, isocyanate-free, low in VOCs, and free of hazardous air polluting (HAP) solvents, will be based on non-hazardous raw materials and will be formulated as single- (1K) and two-component (2K) systems. The project will involve of manufacturer scale-up topcoats in multi-gallon quantities, verifying their performance in a laboratory setting in accordance with military specification requirements, demonstrating these new topcoats on in-service surface ships and submarines, and validating they provide equivalent or greater performance compared to currently qualified topcoats.
Polysiloxane topcoats were transitioned by the Naval Sea Systems Command in the early 2010’s to replace the 50-year-old silicone alkyd coating technology that was used to provide camouflage on the exterior of surface ships. These coatings are qualified to MIL-PRF-24635 and have many performance benefits over silicone alkyds, including improved corrosion resistance (two-coat vs. three-coat system), greater color and gloss retention, and improved adhesion to anti-corrosive epoxy primers. The 1K polysiloxane topcoats for ships and submarines are based on novel polymers with a flexible aliphatic backbone and terminal alkoxysilane groups. The 2K polysiloxane topcoats are based on the dual-reaction of epoxy-functional oligomers with amine-functional oligomers, including hydrolysis and condensation of aminoalkoxysilanes to form a cross-linked network. Both the 1K and 2K polysiloxanes are formulated with a unique blend of environmentally friendly solvents, fillers/pigments, and additives that enable the removal of Oxsol 100 while retaining flash point >100 °F. These formulas also do not require the use of isocyanates to provide highly flexible systems. All of the raw materials used in these environmentally friendly topcoats will be commercially available and registered under the EPA’s Toxic Substance Control Act.
Implementation of Oxsol-free and low-VOC polysiloxane topcoats for surface ships and submarines will enable the fleet to use coatings that are compliant to impending regulations surrounding toxicity concerns, in addition to eliminating the environmental and health risks associated with exposure to isocyanate-based molecules. This project would also provide a path forward for the Department of Defense for modifying other coating systems, such as MIL-DTL-24607 (interior chlorinated alkyd), which also contains Oxsol. Furthermore, the lifecycle cost of submarine topcoats will be reduced since the polysiloxane topcoats have shown to provide significantly greater color and gloss retention than the polyurethanes qualified to submarine requirements. Finally, implementation of a 1K topcoat for all exterior painting will enable sailors to perform touch-up and repair applications with a topcoat that is user-friendly and generates minimal hazardous waste, unlike the current 2K systems that require mixing before application and generate hazardous waste from unused mixed material.