How to formulate coatings with dirt pick-up resistance (DPUR)?

Often, additives are the culprit behind the stickiness of the coating surface. They make the film water sensitive and thus more sticky. In cases of additives failure, the additives sweat out or leach out on the surface. Most common additives that are behind this are: rheology modifiers, dispersing agents, coalescing agent (when it evaporates slow, it makes the film sticky).

Image credits: CPHC Limited^a

• It is essential to check the water sensitivity of the coating film because such coatings tend to absorb water more readily. This leads to:
  • Softening: This makes it more susceptible to picking up dirt particles that become embedded in the softer surface.
  • Swelling: Water absorption can cause the coating to swell slightly, potentially creating microscopic cracks or imperfections on the surface. These imperfections can then act as traps for dirt particles.
  • Breakdown of binding polymers: In extreme cases, water sensitivity can lead to the breakdown of the binders holding the coating together. This breakdown can cause the coating to become flaky or powdery, making it even more prone to dirt pick-up.
• Complete film formation must be achieved. Harder dry film reduces dirt pick up.
• Reduce surface tension of the dried film.