1992 Volume 48 Issue 9 Pages 493-500
Smoothness of paper is customarily measured by an air-leak smoothness tester. An Oken type instrument was used in this work. The purpose of this study was to examine what roughness size level the air-leak smoothness expresses if roughness includes microroughness to macroroughness variously. A profile curve measured by a stylus instrument was separated into waves with various wavelengths by Fourier-transform. Amplitude of each waves was correlated with the Oken type smoothness. From a profile curve measured by a stylus instrument, the centerline average was calculated after removing waviness components which correspond to waves with wavelength conventionally longer than 800 μm. When this cut-off value indicating a threshold level was varied, the centerline average was correlated with the Oken type smoothness. Such correlation analyses connected with spectral analyses were applied for various kinds of handsheet. They include calendered sheets and those made from beaten pulp. As a result, the correlation between the Oken type smoothness and the centerline average with the cut-off value showed a smoother change and a more distinctive peak. Moreover, the roughness level Oken type smoothness expresses was found to be waves with wavelength equivalent to or less than about 273 μm for handsheets.