Prediction of sag resistance in paints using rheological measurements

Sagging in paints is mainly governed by rheology. In this work, two methods are proposed to predict the Anti-Sag Index of paints (ASTM D4400) based on the rheological analysis of the sag flow. Both methods provide good predictions with a characteristic velocity in the range of 400−600 μm/s. The maximum difference between the predicted values of the Anti-Sag Index and the observed ones is ∼2 mils. The viscoelastic properties of paints have also been examined, and a strong correlation is found between the Anti-Sag Index and the elastic modulus in the linear regime, G’, especially the one measured at time zero, immediately after pre-shear, probably because it is more representative of the paint behavior right after the application and the onset of the drying process.