Dynamics of Film Separation in the Printing Process.

The process of film separation during printing must be considered an impact process, in which not the force, but the energy involved plays the major part. The energy of film separation has been measured accurately in a new apparatus under conditions closely approaching those existing on a press. The results indicate that at high speeds film separation cannot occur by simple liquid flow, but is caused by a rupture, against elastic forces. This is due to the fact that the flow response to stress in the exceedingly small period of separation at high printing speeds, of the order of 10-4 - 10-5 seconds, is completely overshadowed by an elastic response. Direct evidence of the elastic character of film separation has been obtained by ultra-rapid micrography, while a quantitative estimation of the magnitude of the modulus of elasticity connected with the reaction to stress of the film has been made by means of vibrating piezoelectric crystals.