Abstract
Relating to the real contact area against a plane smooth surface, frictional properties of coated and uncoated papers were examined under varying applied pressure. An optical interference method using a scanning laser microscope was adopted to measure real contact area against a plane glass plate. The real contact area of the coated paper increased nearly in proportion to the apparent pressure over a wide range of pressure. From the theory of tribology, this result shows that the contact of coated paper is rather plastic and this fact could explain the constant coefficient of friction with increasing apparent pressure. On the other hand, the contact of uncoated base paper was generally elastic and this fact was one reason for the decrease of the coefficient with increasing apparent pressure, shown in the previous report. In addition, an electron spectroscopy for chemical analysis (ESCA) was employed to examine the thickness of binder on pigment particles from the chemical composition at the exact coating surface, because the frictional behavior and the real contact area seemed to depend on the surface material. The result of ESCA suggested that the binder covered the pigment surface enough to control the frictional behavior, and further that the binder existed mainly at the border region between the pigment particles and partly covered the surface of pigment particles.
