The open time of latex paints is an important parameter used as a guideline by painters to approximate the time remaining for applied paint to be sufficiently wet and fluid to smoothly blend in with subsequent and overlapping application of additional paint. Ignoring open time guidelines could lead to imperfections or defects in the dry paint film that may require sanding and adding an additional topcoat over the problem area. The current industry standard to test open time of latex paints is ASTM D7488-11. This standard method can have varying results from user to user due to differences in skill level, temperature, humidity, and/or the subjective nature of the test results. These factors call for creating an empirical method to reduce the amount of variation and provide a more accurate time for an applicator to use. A rheometer is a sophisticated instrument that is used to study flow properties of latex paints and can also be used to study the drying process. The method involves monitoring the viscoelastic properties of the paint sample over time.  As paint dries, water evaporates, and a film begins to form, causing the sample to become more elastic and less viscous. This is translated from the rheometer as an increase in the storage modulus (G’). In this study, there was a correlation between the open time observed through ASTM D7488-11 and an oscillatory test that maintained a constant strain and frequency while a paint sample dried.

Latex paint open time analysis through rheological methods

2019 Fall National Meeting

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