Coating rheology

Rheology, that is, the flow and deformation properties of coatings, including viscosity, thixotropy, yield value and flow curve. We all know that when the paint is stirred or shaken, the viscosity will decrease, but after stopping the stirring and standing for a period of time, the viscosity will rise again. 1. This property of coating is the so-called "thixotropy", which is the main content of rheology.

To measure the thixotropy of coatings, a Rotational Viscometer can be used. Its structure is generally two concentric cylinders, the gap between the cylinders is small, and one of the two cylinders can be rotated. It can be driven by a motor, and the speed can be adjusted. The internal cylinder rotates at a given low speed (about 6 to 120 revolutions per minute), so that the flow conditions of the liquid are consistent with simple motion. Measuring the torque caused by the inner cylinder on the outer cylinder can be converted into an absolute viscosity value.

When measuring thixotropy, an appropriate rotor can be selected according to the viscosity range of the paint. First start at low speed, gradually increase the speed, and read each reading; then gradually decrease the speed and measure again, also record each reading, and multiply each reading by a specific coefficient in the coefficient table to obtain the absolute viscosity (centipoise). After plotting, a circular curve can be obtained, which represents the thixotropy and its size of the tested paint.