Reduction of the Effect of Drying of Acrylic Paint During its Rheological Characterization

Samples containing solvents such as paint or ink can be challenging to measure, as the material will dry up when in contact with air. Consequently, the measurement time may have to be shortened and sample handling becomes more difficult. However, by using a solvent trap, this evaporation can be significantly reduced.

Rheological measurements of paints, inks and lacquers are subjected to drying effects due to the evaporation of water or other solvents contained within the sample. This evaporation immediately sets in when the sample is in direct contact with air. In terms of rheological parameters, drying can, for example, be described by a rapid increase of the viscosity η or a sudden drop in the phase angle δ.

Since these effects impair the actual measurement, evaporation of solvents within the sample should ideally be delayed until the test is completed. However, shortening the measurement time to address this problem usually leads to less accurate and less reliable results and more difficult sample handling.

Alternatively, a solvent trap can be used (Figure 1, Figure 2) which reduces the convection around the sample. Suitable upper measuring systems contain a reservoir at their top surface which can be filled with water or other solvents. Along with the geometry of the solvent trap, this effectively reduces the convection that causes the drying. Additionally, once the solvent contained in the reservoir starts evaporating, the air underneath the trap (i.e. surrounding the sample) will be enriched with the corresponding component. Because of this, the sample will dry slower than at ambient conditions. 

This report shows how a water-based acrylic paint can be efficiently characterized using a temperature device PTD 180 MD along with a solvent trap.

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