Surface of Coated Papers Studied by AFM - Influence of Plastic Pigments on Microstructure and Gloss, 1998 Coating Conference Proceedings

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AFM is powerful nondestructive method, that yields an insight in surface structure and roughness of coated papers. It combines very high resultion in z- with the high resolution in xy-direction even on fragile samples such as paper. Due to the fine measuring tip - in contrast to the profilometer - features in the nanometer regime can be resolved. It not only provides suitable roughness values, but the important advantage of AFM is to visualize material contrasts and thus better understand the coating surface structure and the factors influencing roughness. Only with AFM can topography and chemical information be recorded simultaneousely. With AFM it is shown, that calendering induces an asymmetric deformation of the coating. Mainly the hills are flattened, while the valleys remain relatively unaffected. In the investigated cases during the first NIP, the valley depth decreases only 25%, while the peaks are flattened to 50% of their original height. Further calendering reduces valleys and peaks to nearly the same degree. The asymmetry is mainly induced in the early stages of calendering. Utilizing these techniques, the effect of plastic pigments on the surface roughness was elucidated. The thermoplastic property of the polymer allows an even better flattening of the surface. The plastic pigment itself is flattened, giving a remarkable increase in the total flat surface area.