Coatings are viscoelastic. This means that they change their properties depending on time and temperature: Initially they behave more like liquids, later more like solids. Viscoelasticity, in turn, is crucial for predicting the leveling, i.e. the ability of a coating to compensate for unevenness.

A wealth of data is required to simulate this complex behavior of paints. The measuring devices that provide this data are called rotational rheometers. They determine the flowability of paints by causing a thin liquid paint sample to rotate or vibrate with an attached disk and then measuring the force required for deformation. However, existing devices prevent the solvents from evaporating, meaning that the results are only of limited use to the paint industry. This is why Dr. Fabian Seeler, a researcher at the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA), and his team have developed a new measuring technique.

They copied the measuring principle from the bat. The bat uses short ultrasonic calls for orientation: each call contains low and high frequencies that are reflected by the environment and merge smoothly into one another. The bat uses the echo to recognize where obstacles or prey are located, for example. By repeating the call, the bat can track how the distance to an obstacle changes over time or how the prey moves.

The PaintVisco rheometer also works with smoothly merging frequencies. The frequencies with which the paint sample is deformed are varied. By repeating the sequence of frequencies, the change in viscoelastic paint properties during setting can be recorded. Dr. Seeler emphasizes that this signal form makes it possible to determine all the data required for the progression prediction within a very short time.

With the virtual paint laboratory, the researchers at Fraunhofer IPA can now also take solvent evaporation into account: In their rheometer, the paint layer is no longer deformed by a closed disk, but by a construction of several rings. The openings between the rings allow the solvent to evaporate.