An investigation of the friction properties of coated paper

Paper-paper friction of papers coated with different coating formulations was measured according to ISO 15359. Both pilot-coated papers and laboratory-coated papers were used. The measurements on the laboratory-coated papers revealed that the pigment had the greatest influence on the friction properties. Papers coated with ground CaCO(3) pigments had friction coefficients between 1.5 and 2 times higher than those of similar coatings based on kaolin clay. The choice of latex had a rather small influence on the friction. Paper coatings containing styrene-butadiene latex as binder exhibited a slightly higher friction than coatings containing poly(vinyl acetate) latex. The grammage of the coating had no influence on the friction coefficient in the investigated coat weight range of 10-15 g/m(2). Calendering had no appreciable influence on the friction properties. In the pilot coating, both ground and precipitated CaCO(3) pigments were used. The shape of the pigment particles was found to have some influence on the friction coefficient, which in a sense confirmed the results obtained with the laboratory-coated papers, where differences between clay (platy particles) and ground CaCO(3) (isometric particles) were noted. In case of the pilot-coated papers, the measuring direction in the friction tester also had an effect. The results indicated that the friction properties of coated paper depend strongly on the microstructure of the coating surface. It may indeed be argued that the microstructure of the coating is more important than its surface energy. This is primary because the surface energy of the coating layer is determined by that of the latex, which does not vary very much among the latices used in practice.