Final Report: Chromium-Free Corrosion-Resistant Hybrid UV CoatingsEPA Contract Number: EPD09029
Title: Chromium-Free Corrosion-Resistant Hybrid UV Coatings
Investigators: Curatolo, Ben
Small Business: Light Curable Coatings
EPA Contact: Richards, April
Project Period: February 1, 2009 through July 31, 2009
Project Amount: $69,997
RFA: Small Business Innovation Research (SBIR) - Phase I (2009) RFA Text | Recipients Lists
Research Category: SBIR - Pollution Prevention , Small Business Innovation Research (SBIR)
This research project established the feasibility of preparing an environmentally friendly chromium-free solvent-free hybrid UV coating system suitable for industrial, automotive, and aerospace corrosion resistance applications. In particular, an appropriate segregation of components was determined for a two part chromium-free corrosion-resistant hybrid UV coating system that gave good protection to 2024-T3 aluminum alloy panels in ASTM B-117 salt fog testing. This hybrid UV coating system contained an appropriate ratio of reactive groups to provide immediate cure when exposed to UV light along with a secondary cure mechanism that was active in the absence of UV light. Coatings demonstrated the ability to be masked with tape immediately after UV cure, and de-masked later without marring. This system demonstrated a suitable rate of cure in the absence of UV light to dry overspray to reduce the possibility of contamination from spray painting operations and to dry material in shadow areas where the coating might not be exposed to sufficient UV energy for typical UV cure. The secondary cure mechanism in the absence of UV light also could be useful to provide a system with significant surface hardness development after processes such as sanding of paint primers that could be adversely impacted if high surface hardness was developed too soon. An important aspect of this proprietary technology is the potential to significantly reduce exposure of workers and communities to hexavalent chromium, volatile organic compounds (VOCs), and hazardous air pollutant (HAP) materials.
The two part chromium-free solvent-free hybrid UV coating system was characterized with respect to UV cure rate, secondary cure rate, adhesion, surface hardness, solvent resistance, and corrosion resistance. Both gray formulations and white formulations were prepared. The hybrid UV coatings immediately became tack-free upon exposure to UV light, and immediately demonstrated good adhesion. Coatings demonstrated the ability to be masked with tape immediately after UV cure, and de-masked later without marring. Pencil hardness improved with time as the secondary cure mechanism proceeded after the UV exposure. The coatings exhibited good solvent resistance as evidenced by resistance to over 200 double rubs with methyl ethyl ketone (MEK), and the coatings also maintained their integrity after a 24 hour soak in Skydrol hydraulic fluid. Two part gray hybrid UV coatings and two part white hybrid UV coatings, each containing a chromium-free corrosion inhibitor, were applied to duplicate 2024-T3 aluminum alloy panels, cured, scribed, and placed into ASTM Test Method B-117 salt fog testing to determine corrosion resistance. After 1,000 hours, the scribe lines were still shiny for the hybrid UV coating panels. For some panels, there was no evidence of blisters, salting, or any corrosion at all, and on some of the panels there were a few small blisters. Control panels without the corrosion inhibitor demonstrated significant corrosion, including scribe darkening, salting, and blistering. This indicated that the chromium-free corrosion inhibitor was active in this two part hybrid UV coating system.
This Phase I SBIR project demonstrated the feasibility of a new proprietary two part hybrid UV coating system that incorporated a chromium-free corrosion inhibitor and a secondary cure mechanism into a UV curable coating to enhance the capabilities of the system. The first part of the hybrid cure system resulted in immediate tack-free surfaces and significant properties through UV cure which allowed coated materials to be handled for secondary operations. The second part of the dual cure continued at ambient conditions without the use of ovens or infrared radiation, at a slower rate for reduced stress and improved physical properties, including surface hardness. The enhanced capabilities of this solvent-free hybrid UV coating system included chromium-free corrosion resistance as well as appropriate adhesion, surface hardness, solvent resistance, and the ability to cure in the absence of UV light to dry overspray from painting operations and to dry material in shadow areas where the coating may not be exposed to sufficient UV energy for typical UV cure. Together with the environmental and performance advantages of UV curing, incorporation of a chromium-free corrosion inhibitor and appropriate functional groups for secondary cure extended the applicability of this hybrid system to numerous industrial, automotive, and aerospace applications requiring corrosion protection. Demonstration of the feasibility of this two part chromium-free corrosion-resistant hybrid UV coating system provided the basis for a more complete evaluation according to the major appearance and physical property requirements of aerospace primer specification MIL-PRF-23377 and aerospace topcoat specification MIL-PRF-85285.
Potential commercial applications of this chromium-free corrosion-resistant hybrid UV coating technology include industrial, automotive, and aerospace coatings for corrosion protection. Anticipated benefits of this technology include improved environmental friendliness, efficiency, and productivity capabilities. Since this hybrid resin system contains safer components, application in confined spaces and occupied spaces should be possible without the hazards presented by conventional materials. Environmental savings apply not only in production, but also throughout and beyond the operational lifecycle of vehicles and industrial products by reducing environmental risks associated with maintenance, storage, and disposal. In addition to the known environmental and efficiency advantages of standard UV technology, this hybrid system offers additional advantages such as the ability to cure overspray to reduce the possibility of contamination from spray operations, the ability to cure in shadow areas, the ability to mask and de-mask painted surfaces after tack-free cure but before full coating property development, and the ability to easily sand paint primers before full hardness development. This technology offers a significant positive societal impact in terms of a better quality of life for industrial workers and for citizens through safer workplaces and a cleaner environment.