Structure recovery, surface levelling and flow behaviour of coatings

The quality of a coating is directly related to its time-dependent rheological behaviour, which can be measured by means of a three-interval thixotropy test (3ITT).

Structure recovery, surface leveling and flow behaviour are key quality characteristics of coatings. These processes are referred to as ‘thixotropic behaviour’ and are largely responsible for whether a product is positively or negatively judged by the user. The thixotropic behaviour of coatings cannot be determined with flow curves generated with spindle or cylinder systems or with flow viscosities measured with flow cups (DIN EN ISO 2431).

A suitable test for the direct measurement of the structure recovery of a coating following shear stress is the three-interval thixotropy test (3ITT). The experimental set-up closely simulates the application process, with three measuring periods that simulate the behaviour of paints at rest, their behaviour during the application, and the structural recovery after application.

Download the application report available from Anton Paar to see how measurements with a rotational rheometer are used to determine the thixotropic behaviour of coatings for quality control.