Impact of an ink drop on paper

Dynamical spreading of an ink drop impacting on paper has been investigated experimentally. Ink drops of various sizes and velocities, impacting on paper, were observed by a microscope with stroboscopic lighting. Experimental data are explained well by a simple correlation formula, which predicts the ratio of spreading as a function of the Weber number and the Reynolds number. This experimental formula can be conveniently used in the design of ink jet printers.