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

• Main Author: Boke, Jason W
• Format: Others
• Published: DigitalCommons@CalPoly 2013
• Subjects: titanium dioxide; spread rate; calcium carbonate
• Online Access: https://digitalcommons.calpoly.edu/theses/999; https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=2065&context=theses

Titanium dioxide (TiO2) is an essential component in a white paint formulation due to its excellent light scattering ability. TiO2 also happens to make up most of the raw materials cost. Viable replacements to TiO2 do not currently exist in a feasible manner. Rising costs in the recent TiO2 supply shortage have forced coatings formulators to find a balance between cost and performance. One method includes partial substitution of TiO2 with cheaper material such as calcium carbonate (CaCO3), which serves to occupy volume. The purpose of this study was to compare the coating spread rate of paints with varying TiO2 and CaCO3 pigment volume concentration (PVC). Different sized CaCO3 particles were used in this study. A series of PVC ladder studies were performed at keeping CaCO3 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. It was found that replacement of up to 20 PVC of TiO2 with CaCO3 could marginally increase the spread rate, thus increasing the efficiency of TiO2. 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.