SHORT-TIME COATING DEWATERING: A NOVEL TEST METHOD AND MODEL, 2008 Advanced Coating Fundamentals Symposium

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The rate of coating dewatering is critical for trouble free operation of coating processes and is expected to influence the quality of the final product. Current methods to characterize this rate form a thick filtercake and over 30 seconds of time. There is a need to determine if these long- time tests represent what is happening in the millisecond contact time in a coating process.

A novel method is proposed that can characterize the rate of dewatering on the order of 10 ms. Four different methods to characterize the rate of dewatering are compared for several different suspensions and coatings. All give similar trends between various suspensions ranking the rapid and slow dewatering systems correctly. However, when the Darcy permeability coefficient is calculated from the data, the values are two or three orders of magnitude different. The methods with short contact times give high values of the permeability. This may be caused by a more open filtercake that is formed for the first few layers of particles. The rheometer method gave coefficients that are quite small; shear and long time dewatering may generate a dense filtercake. One standard method gives permeabilities that are of the same order of magnitude as the Blake-Kozeny equation.