Bayer MaterialScience LLC reported at last week’s American Coatings Show and Conference that field trials confirm the application effectiveness of a new, thick-film, moisture-cure urethane technology for high-performance protective coatings used on structural steel in corrosive environments.
Bayer R&D Specialist Ahren Olson, addressing a program session at the ACS conference, reported that coatings based on the polyurethane technology can be effectively applied at up to 8 mils dry film thickness (DFT), with sag resistance at thicknesses of 10-12 mils. Olson said currently available aliphatic moisture-cure urethane topcoats are typically applied at 2-4 mils DFT.
Olson reviewed experimental design, resin development, and supporting field trials in an AC Conference technical presentation, “Developing and Field Testing High-Build Aliphatic Moisture-Cure Coatings.” The coatings discussed were formulated with the use of a new aliphatic HDI/IPDI prepolymer developed for high-build moisture-cure urethane coatings used to protect structural steel in such corrosive environments as bridges, water and waste tanks, treatment plants, marine environments, chemical plants, offshore oil and gas piping, and others, the company said.
Olson said two separate field trials using the high-build technology have been successfully completed in two separate climates. In hot and humid conditions (97 F and 50% humidity), the high-build MCU topcoat was applied up to 5 mils DFT. In cooler, more typical MCU application conditions (55 F and 72% humidity), up to 7 mils DFT was successfully applied.
The moisture-cure urethane is more tolerant of high temperature and high humidity conditions, providing opportunities for use in southern U.S. climates, said Ed Squiller, director—business development, coatings, adhesives and specialties, Bayer MaterialScience. Coatings based on the technology also are one-component materials, which simplifies application procedures, he added.
Squiller, discussing the technology during a meeting with representatives of PaintSquare News and the Journal of Protective Coatings & Linings (JPCL), said the capabilities of coatings based on the technology make the coating less prone to defects such as blistering when applied at greater thicknesses. Such defects can be a common occurrence in moisture-cure coatings applied at thicknesses that exceed recommended levels, he said, adding that such excessive coating build is not uncommon in the field.
Moisture-cure urethane coatings consist of a polyisocyanate-functional resin formulated with solvents, pigments, and additives in a one-component product. The paint cures as the isocyanate resin reacts with ambient moisture after being applied to the substrate. Such coatings are able to cure at low temperatures if ambient moisture is present, and are also characterized by a high degree of surface tolerance. One-component paint systems also eliminate the possibility of mixing errors in the field involving multiple coating components, which can cause problems with coatings cure and performance properties.