Calcium Carbonate Particle Size Effects on Titanium Dioxide Light Scattering in Coatings

Titanium dioxide (TiO 2) is an essential component in a white paint formulation due to its excellent light scattering ability. TiO 2 also happens to make up most of the raw materials cost. Viable replacements to TiO 2 do not currently exist in a feasible manner. Rising costs in the recent TiO 2 supply shortage have forced coatings formulators to find a balance between cost and performance. One method includes partial substitution of TiO 2 with cheaper material such as calcium carbonate (CaCO 3), which serves to occupy volume. The purpose of this study was to compare the coating spread rate of paints with varying TiO 2 and CaCO 3 pigment volume concentration (PVC). Different sized CaCO 3 particles were used in this study. A series of PVC ladder studies were performed at keeping CaCO 3 PVC constant. Paints were formulated at the same volume solids to minimize variability. Weighed coating draw-downs were prepared to measure the contrast ratio. The coating spread rates were obtained with the DuPont Spread Rate program, which relies on Kubelka-Munk relationships, which takes into account the physical properties of the paint. These spread rate values were compared to one another across type and size to find common trends. Critical pigment volume concentration (CPVC) values were determined through regression of the spread rate values and compared to oil absorption tests. v It was found that replacement of up to 20 PVC of TiO 2 with CaCO 3 could marginally increase the spread rate, thus increasing the efficiency of TiO 2. The spread rate increased modestly as similarly sized extender particles were initially introduced, then dropped at higher extender levels. Data analysis revealed that CPVC was influenced based on the size and amount of the extender particle present, which can be used to predict resin demand of a paint system. vi ACKNOWLEDGMENTS I would like to thank E. I. du Pont de Nemours and Company, particularly Dr. Michael Diebold for the opportunity as well as introducing me to the wonderful world of white pigment technology. I also thank Dr. Raymond Fernando for his support when I first learned about the Polymers and Coatings Program as well as Dr. Kevin Kingsbury for serving on my advisory committee. Finally, I want to thank the Bill Moore Fellowship Fund for financial support and the Polymers and Coatings Program for making everything possible.