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Phenomena affecting ink transfer in offset lithographic printing. / Georgios Vlachopoulos

Swansea University Author: Georgios Vlachopoulos

Abstract

The ink transfer mechanisms in the offset lithographic printing process is consisted by a complex inking roller train which a series of alternately rigid and deformable rollers, are used to precondition and deliver the printing fluid from the ink and fount reservoirs to the image carrier. The lithog...

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Published: 2010
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42395
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Abstract: The ink transfer mechanisms in the offset lithographic printing process is consisted by a complex inking roller train which a series of alternately rigid and deformable rollers, are used to precondition and deliver the printing fluid from the ink and fount reservoirs to the image carrier. The lithographic printing inks are complex formulated non-Newtonian fluids with high viscoelastic rheological profile and thixotropic behaviour. A set of ink dilutions was produced based on coldset lithographic printing ink diluted in concentration with Butyl-Diglycol. The rheological profile of the produced inks was examined by detailed rheological characterisation with particular interest on viscosity on tack, thixotropy, viscoelasticity, surface tension, extension and shear viscosity. Further examination established the relationships between shear viscosity and tack focusing on a printing nip between a rigid and elastic roller. A decrease in tack was found to be associated with a decrease in shear and the apparent extension viscosity. Developed imprinting and photographic techniques used to capture and characterise the fundamental phenomena of ribbing and misting associated with ink film splitting at the rollers nip in offset printing. Such techniques used to capture the dynamic profile of those mechanisms on a closed loop distribution system by using a tack meter. The detailed profile of those phenomena was characterised with particular interest on the relationship with the fluids rheological profile and the Capillary number. Extension rheometer was also used to analyse the mechanisms of ribbing and misting phenomena by experimental simulation of a printing nip. A factorial experiment was undertaken based on LI8 Orthogonal Array techniques. The parameters of rollers ratio, ink film thickness, temperature, distribution speed, distribution time and inks viscosity were found to have an influence on misting and ribbing phenomena. Results and analysis established responses and interactions between the process parameters but also between ribbing and misting as essential phenomena with the ink transfer mechanisms in lithographic printing process.
Keywords: Mechanical engineering.
College: College of Engineering