Fraunhofer IPA: Paint savings with the bat as a model
How long does the paint remain flowable? How well does it level out unevenness? Under what conditions does the desired mirror-smooth surface form? “Until now, painters had to try out in costly and time-consuming trial-and-error experiments when a paint layer runs optimally,” explains Dr Fabian Seeler. In the Paint Visco project, he has now developed a simulation programme that can be used to virtually determine the properties of paints.
The development of the computer model was a challenge for the Fraunhofer IPA researcher and his team due to the viscoelasticity of the paints. The viscoelasticity, in turn, is decisive for predicting the flow, i.e. the ability of a paint to compensate for unevenness – this can be superficial brush marks, but also pores, wave structures and edges under the paint layer.
New measuring technique
Rotational rheometers determine the flowability of paints by causing a thin liquid paint sample to rotate or oscillate with a disc attached and then measure what force is needed to deform it. “However, previous devices prevent the solvents from evaporating, so the results are of limited use to the paint industry. In addition, such measurements always show only a small, arbitrarily selected section of the material behaviour, since often only one vibration frequency is measured,” reports Seeler. For computational projections, however, one needs much more comprehensive information about the material behaviour, for example the behaviour of a paint sample at numerous frequencies.
Together with his team, he has developed a new measuring technique. Nature was the inspiration: “We copied the measuring principle from the bat,” the researcher recalls. Like the bat, the Paint-Visco-Rheometer works with frequencies that flow into each other. However, it is not ultrasonic calls that are varied, but the frequencies with which the paint sample is deformed. By repeating the sequence of frequencies, the change in viscoelastic paint properties during setting can be recorded. This special signal form makes it possible to determine all the data needed for the progression prognosis within a very short time, Seeler emphasises.
With the new measuring technique, the researchers at Fraunhofer IPA can now also take into account solvent evaporation, which is important for industry: In their rheometer, the paint layer is no longer deformed by a closed disc, but by a construction of several rings. The openings between the rings allow the solvent to evaporate.