Effect of Stylus Size on Surface Roughness Characterization of Paper Products

Abstract

Surface roughness plays a critical role in determining the performance and quality of paper products; however, its accurate determination depends strongly on the geometry of the stylus used in contact profilometry. Herein, the effect of stylus-tip size on surface roughness characterization was evaluated along with the suitability of fractal dimension (FD) analysis as a supplementary metric. Styluses with tip radii ranging from 0.25 to 1.75 mm were examined, and a 0.5-mm stylus tip (0.5R) yielded the most stable and reliable surface roughness measurements under a constant contact force of 5 gf. Coating considerably reduced surface roughness fluctuations, with the roughness mean absolute deviation (RMAD) decreasing by 78%. A comparison between a 0.5R conical stylus and a pyramidal stylus showed strong agreement in the R_a and RMAD values, confirming that the conical design maintained minimal contact area. High-resolution profilometry (0.1-μm spacing distance and 200,000 data points per scan) enabled the computation of FD via power spectral density analysis. FD values approached 2 for coated paper, reflecting a transition from line-dominated to more areal surface structures. These findings indicate that stylus selection critically affects surface roughness characterizations and that FD serves as a useful complementary descriptor for surface roughness changes.