Printing Dynamics: Nip Pressure and Its Relationship with Materials' Viscoelasticity

摘要

A theoretical framework of nip dynamics of conventional printing, including dynamic models deducted from nip geometry, printing speed, and physics laws, is proposed. Different from previous works, the present work focuses at obtaining the nip pressure from a given nip geometric setting, the common way in full-scale printing. The effects of viscoelastic characteristics of paper substrate and print form (rubber and/or polymer) on the nip pressure, which become pronounced in a full-scale printing process due to high speed, are accounted and illustrated by three physical models, e.g., Maxwell model, Kelvin-Voigt model, and Burgers model. Details of the nip dynamic features, shape, amplitude, duration, and effective nip width, etc., have been worked out. The viscoelastic nature of the materials was found to be responsible for the so-called speed-hardening, asymmetric nip profile, variations in the nip amplitude and effective nip width, etc. It was also found that how the viscoelastic properties of the materials affect the nip dynamics depend on the how the elastic components and the viscos count parts are connected with each other. The framework is applicable to calendaring, gravure, offset, and flexography.