Platform for measuring internal stress and thickness of drying paint

Watching paint dry

fredag 09 nov 18
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Kontakt

En Te Hwu
Lektor
DTU Nanotech
45 25 68 43

Kontakt

Peter Emil Larsen
Postdoc
DTU Nanotech
45 25 57 28

A novel method for measuring internal stress in drying paint has been developed by researchers at DTU Nanotech.

In the modern world, paints are everywhere, protecting cars and ships against corrosion, wood from weather conditions etc. To fulfil its purpose, the paint layer needs to be free of surface defects. The new method developed by DTU Nanotech researchers provides a better understanding of the processes leading to formation of cracks in paint layers.

Why does paint crack?

One of the main causes of crack formation is internal stress in the paint, which is the result of chemical curing and solvent loss in the wet film applied on a surface. Small local variations lead to a non-uniform distribution of stress, which can make the likelihood of defects hard to predict. On top of that, high local stress is more likely to make a paint layer more fragile and sensitive to external forces, e.g. temperature change, humidity, mechanical force.

Standard method for measuring is flawed

Frequently, the creation of stress in paint layers is measured by coating thin long metal strips with a given paint and calculating the resulting stress from how much they bend during paint curing. This method has two drawbacks. First, in real applications paint would typically be applied to a solid inflexible surface. This limits the conclusions that can be drawn from the experiment. Secondly, the experiments only give insight into the final stage of the fully dried paint. No information is obtained of the processes during the actual curing period.

Novel method provides new insights and higher accuracy

The new method uses millimetre-scale cantilevers to make the measurements. After coating a metal shim, the novel platform measures the microscopic bending caused by the creation of internal stress. The measurements are contact-free as they rely on advanced image processing algorithms analysing microscope images of the shim from the side. The method stands out from previous approaches because it addresses all the issues mentioned above. The microscopic bending of the shims is much closer to real applications. The measurements are performed throughout the drying process, resulting in much deeper insights into the internal processes leading to the creation of internal stress. Finally, the small scale of the shim enables investigation of local inhomogeneity.

New method for measuring durability of paint

A new platform for measuring durability of paint (Photo by Jesper Scheel)

Associate Professor En-Te (Edwin) Hwu, Postdoc Peter Emil Larsen from DTU Nanotech and Senior Chemist Saif Ullah with his team from Hempel have together developed this new method for measuring the durability of a paint. The overall aim of the project is to get a better understanding of what happens in the curing process of paint enabling development of more resilient products.

En-Te Hwu and Peter Emil Larsen are part of Anja Boisen’s research group at DTU Nanotech.

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