Printing Dynamics: Nip Pressure and Its Relationship with Materials\u2019 Viscoelasticity

Li Yang

doi:10.1007/s41783-020-00091-z

Abstract

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.

Highlights

E.g., offset and flexography, ink transferring from a print nip to a paper surface relies on mechanical contact between the print form and the paper surface [1]
The existing studies focused on finding deformation behavior with respect to a known loading condition, while the present study focuses on finding the nip pressure when the deformation of the material is known or defined by the nip geometry
The focus will be given to the dynamic interactions between the nip and the material stack that passes through the nip

Summary

Introduction

E.g., offset and flexography, ink transferring from a print nip to a paper (board) surface relies on mechanical contact between the print form (nip) and the paper surface [1]. The expression for the nip pressure as a function of viscoelastic characteristics of the materials involved, e.g. paperboard, rubber blanket, and polymer plate, etc., in addition to the geometrical settings, printing speed etc., has been worked out. The existing studies focused on finding deformation behavior with respect to a known loading condition (stress), while the present study focuses on finding the nip pressure (the stress) when the deformation of the material is known or defined by the nip geometry Another difference is the speed of deformation as the material undergoes rapid deformation amid to high printing speed, up to 10 m s−1 in a full-scale flexographic printing. As worked out in the Appendix, the four unknowns of the general solution given in Eq (19) can be obtained by solving the linear equations:

Results

Discussion

Conclusion