Wrinkle Formation During the Web Motion in Offset Presses - An Intregal View

A phenomenon that is dreaded and mostly difficult to control by printers is the wrinkle formation of a paper web. Many projects have tried to find models to make the mechanism of the wrinkle formation tangible and conceivable. Also the complicated mechanical and dynamic models failed in practice because of the necessary material parameters like transversal web force and shearing modules were impossible to determine. Simple approaches basing on mostly zonal tension fluctuation do make the problem comprehensible but are still not quantitatively elusive. An integrated view of external forces, internal stress conditions, the image dependent moisture pick-up and web material typical characteristics like the penetration behavior and the fluctuant main orientation of the printing material grain in concur with external temperature influences, as well as construction-related path length within printing machines is necessary. This presentation will show the different importance factors, their reciprocative conditionality and the opportunities of a prediction of wrinkle formation by means of modern paper evaluation methods. Still unusual but technically feasible possibilities in the field of mechanical spreader appliances and dryers will be pointed out.