10.1 - A novel approach to quantify the spatial coating layer formation

A straightforward correlation of coating thickness and base sheet surface height (topography) data does not clearly show the expected differences between application systems - a contour coat like structure for curtain coating or a leveling coat like structure for blade coating. Therefore a measure to clearly distinguish between these different kinds of spatial coating layer formation was defined. Filtering in the frequency domain is used to preserve only the large structures in the coating layer thickness and the base sheet topography data. The coefficient of determination (R²) and the slope of a linear regression model between filtered coating thickness and base sheet surface height (topography) are used as measures describing the leveling behavior of a coating layer. A comparison of three application systems - blade, film-press, and curtain coating - demonstrates the need for as well as the applicability of the proposed method. Analysis of the original data shows only minor differences in the coating layer formation between the application systems. For the filtered data where large structures are preserved, curtain coating was found to give an almost ideal contour coat, where the coating thickness is hardly influenced by the base sheet topography. On the other hand, the coating thickness in blade coating strongly depends on local base sheet surface height variations. A film press application of the coating layer results in a coating structure in between curtain and blade coating.