Industrial maintenance coating formulators are investing time and money in research and development to keep up with increasingly stringent levels of permissible volatile organic compound (VOC) emissions. VOC emissions react with heat and sunlight to form ground-level ozone, and failure to comply with federal, state and local clean air restrictions can result in large financial penalties.
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Manufacturers are finding that reducing VOC emissions is easy compared to the challenge of maintaining coating performance. For this, they’re turning to cutting-edge technologies and, in the meantime, some also are working to change the regulatory paradigm.
Performance compromise: High-performance, industrial-grade coatings need to stand up to caustics, abrasion, chemicals, severe temperatures and humidity. Solvent-based epoxies and polyurethanes are the current favorites, but manufacturers are trying to develop new formulations that have less harmful emissions during application and cure.
They’ve tried using low-VOC resins, removing volatile coalescing solvents, and substituting low-VOC coalescing agents, but the quality of performance tends to suffer. Water-based epoxies and urethanes have poor stability, less surface tolerance and simply don’t perform as well as solvent-based coatings, leading to early corrosion. Water-based coatings require more elaborate surface preparation to ensure proper wetting and adhesion, particularly in dirty or oily environments.
Unintended consequences: Companies such as Rust-Oleum are concerned that excessive VOC restrictions might have unintended consequences. When the South Coast Air Quality Management District (SCAQMD) in California reduced the permissible VOC emissions of industrial maintenance coatings from 250 grams per liter (g/l) to 100 g/l, buyers in the region had to sacrifice performance.
Solvent-based urethane VOC emissions have been brought down to 250 g/l while maintaining performance, but current technology can’t get the levels below 100 g/l at the same level of performance. Latex VOC levels are less than 100 g/l, but urethane and epoxy coatings can last more than 10 times as long as latex coatings, says Scott Cross, Rust-Oleum’s director of marketing.
“Companies in SCAQMD might resort to buying low-VOC latex coatings from the local paint store, but will have to repaint annually,” explains Cross. “This will release emissions every year and increase their surface preparation and maintenance costs – labor makes up 80% of the cost of painting. Additionally, latex coatings are more likely to deteriorate before repainting, which can result in corrosion. This means more steel will have to be manufactured and more steel and structural foundations will have to be replaced, producing a greater burden on the environment. Until technology allows for high-performance properties in low-VOC formulations, any standards below 250 g/l may, in the long run, do more harm than good.”
Rust-Oleum offers several products that meet or exceed VOC requirements in the SCAQMD, including the entire line of Sierra Performance industrial coatings, High Performance and Industrial Choice sprays, Mathys industrial coatings, Concrete Saver, Concrete Protection Systems, and Epoxy Shield products. Although the Mathys product, Noxyde, performs as well as heavy-duty zinc, epoxy and urethane coating systems, it’s a thick mastic coating, which isn’t appropriate for every application.
Next-generation surfactants: Air Products recommends that formulators of low-VOC waterborne coatings use a combined strategy to optimize coating performance: an appropriate polymer, coalescing agent and additive package. Its “next generation” Gemini-type coalescing surfactant (CS) additives improve coalescence, provide low foam and improve substrate wetting. The performance of low-VOC waterborne coatings using the company’s CS technology is said to be similar to their higher-VOC counterparts.
For instance, Air Product’s multi-functional EnviroGem AD01 surfactant is a 100% active, liquid, low-odor, low-foam wetting agent based on Gemini surfactant technology. It imparts little or no VOC to the formulation, significantly reduces surface tension temperature, reduces minimum film formation of dispersion polymers, improves low-temperature film formation, helps to improve wetting and minimizes foam. It essentially functions like a volatile coalescing solvent.
Emerging regulation paradigm: Because individual VOCs aren’t equal in their ozone-forming potential, the American Solvents Council refers to photochemical reactivity as a new paradigm for VOC regulation. This approach distinguishes between more reactive and less reactive VOCs. The higher the reactivity, the greater the potential contribution to ozone formation. The concept, still emerging, could increase coating formulation options and the flexibility to meet performance criteria, while still reducing ozone creation potential.
E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at [email protected].