Dirt-Pickup Resistance In Low Tg Elastomeric Coatings

Maximizing dirt-pickup resistance (DPUR) is a key requirement for many exterior coatings. For example, in roof coatings, aside from aesthetics, maintaining a dirt-free coating can have implications on building energy costs, because a white coating will not absorb as much solar energy as a coating that is soiled. While it is known that higher glass transition temperature (Tg) resins impart improved DPUR, stricter VOC regulations have resulted in using lower Tg resins in traditional exterior architectural coatings. For elastomeric coatings (e.g., acrylics and silicones) that require the use of still softer, low Tg polymers, achieving acceptable DPUR is even more challenging.

This commonly results in reformulation by including special additives or adjusting the coating PVC, which may not be acceptable depending on the application or required coating performance. This study will compare these formulation techniques to resin technology that incorporates DPUR without requiring coating reformulation, particularly in systems with a measured Tg (via differential scanning calorimetry) of less than -10°C. Roof coating formulations developed with an acrylic resin that has a measured Tg as low as -30°C and incorporates this technology is shown to have excellent DPUR in accelerated laboratory testing, compared to similar Tg resins without this technology.

Presented at the Western Coatings Show, October 2021