Encapsulated Toners in Xerography and their Shell Fracture Mechanics

The effect of various elastic and physical parameters on the strength of the shell in encapsulated toner is examined. The contact problem of a toner particle and a pressure roller is discussed, and the mechanism of shell fracture from the viewpoint of Hertz's impact theory is reviewed. The magnitudes of the impact force, the fracturing force, and the paper damaging stress are estimated. Within the framework of linear elasticity theory, general expressions for the stresses induced in the shell and core have been derived for both solid and liquid cores. Particular cases have been computed and presented in normalized graphical form on a unit loading basis. The shell strength depends strongly on the geometrical and elastic properties of the core and shell materials, specifically on the shell thickness, the ratio of the core and shell shear moduli, and the tensile strength of the shell material. The modes of toner fracture and the significant effects of the elastic properties of the paper on the crushing force of the particles is discussed. It is shown that the breaking of the particles is facilitated by a harder surfaced paper.