Studies of Roughness of Printed Surface

Abstract

Surface of printed paper was studied by using a non-contact type surface roughness meter. A black offset ink was transfered on a cast- coated paper, which is the plainest paper traded. In a sample transfered small amount of the ink (y=ca. 0.1gm^-2), ink grains were attached on the tops of unevenness of the paper. Roughness for a center line of the surface (Ra), therefore, is increased from 0.69μm (paper) to 0.82μm, the maximum value. The Ra value was decreased with increasing the amount of the transfered ink to Ra=0.32μm at the sample with 0.8gm^-2 of the ink. This amount of the ink seems to be suitable amount to cover on the paper without deep holes distributed on the paper surface. Over y=1.8gm^-2, the uncovered areas could not be obserbed. The minimum Ra(=0.29μm) value was obtained in the sample with y=3.9gm^-2. Glossy (Gs) of the surface was also measured by the use of a goniometer. Because Gs is in invers proportion to Ra, Gs is closely related with the roughness of the printed surface.