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Evolutions in food packaging printing
You are here: Conferences & Events * 2011 Budapest * Abstracts * 2. Printing Materials

2. Printing Materials

2.01 The role of substrate structure in liquid transfer during heatset offset printing

Carl-Mikael Tĺg, Maunu Toiviainen, Mikko Juuti, Cathy Ridgway, Patrick A.C. Gane

Abstract

Fountain solution transfer to coated papers in a heatset printing process has been evaluated online. The porous coatings, applied as single coating onto a fine paper substrate, were calendered under different conditions to establish a range of porosities and pore structures whilst keeping the formulation, and hence the surface chemistry, constant. The transfer of fount to the papers was analysed from unprinted areas (non-image) and cyan printed areas at six different positions along the printing line, namely between each printing unit and after the dryer section, using near infrared absorption reflectometry. In this way, real time analysis of the amount of fountain solution (defined as water content) transferred to the paper per printing unit as a function of physical paper surface characteristics has been achieved. The role of printing speed and fountain solution dosage level on water uptake by the various coated paper substrates has been investigated. It was concluded that the higher the speed, the less the surface roughness becomes compressed and shorter is the time for the liquid to respond in respect to permeation and capillary uptake, resulting in less liquid transfer. It was also concluded that the image-area of the print functions as a stronger liquid carrier and at the same time hinders the evaporation of the liquid within the internal structure of the paper

Keywords: fountain solution, porous coatings, liquid carrier
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2.02 The effect of coating pore structure and geometry on the drying efficiency of heatset web-offset ink solvent

Philip M. Gerstner,Hai Zhang, Patrick A.C. Gane


Abstract
This work examines the effect of coating pore structure on the evaporation behaviour of mineral oil - a typical ink solvent. Two different kinds of coating pigments are compared, the first one being a standard ground calcium carbonate (GCC), the second one a highly porous modified calcium carbonate (MCC) with fine intraparticle pores, as might be used in offset and inkjet coatings, respectively. The aim is to identify relevant pore structure parameters of the corresponding systems and their effect on the drying rate. Two internal stages of drying were identified for both structures: a rising drying rate period and a falling rate period as temperature is increased. In the rising rate period, the effect of film flow was of particular relevance for the case of GCC based structures: binder, filling the pore structure, decreases the internal surface detail of geometry and thus reduces the film flow tendency, progressively depressing the drying rate. At the onset of the falling rate period the liquid phase is in the form of disconnected liquid clusters. Therefore, the diffusion resistance becomes a dominant factor in determining the drying rate during this latter period. Because of the high permeability of MCC systems the evaporation rate proved to be largely insusceptible to the binder concentration. However, the GCC pigment systems, because of their lower permeability, exhibited an extended peak of the drying rate as a result of the increasing diffusion resistance with increasing binder content.


Keywords: coating structure, capillary vaporisation, film flow, heatset printing
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2.03 Nanoscale single and multilayer adsorption of polyelectrolytes to pulp fibers

Praveen Chandak, Levente Csoka, George Grozdits


Abstract

The paper and printing industry faces the challenges of meeting the changing demands for paper and paper based products. Advances in the electronic media changed the paper needs and affected the paper markets. The news print market started to shrink, while the office printing paper and packaging increased. Printing paper product requirement also changed due to more and more global marketing and the improvements of graphic art and subsequent printing. The new printing industry requires tighter paper structures with smother surfaces.

Poly (diallyl dimethyl ammonium chloride) (PDDA) was used to modify the surface of cotton linter fibers by using the monolayer coating of PDDA  polyelectrolyte on the fibers surface.  Hand sheets were prepared using the polyelectrolyte treated fibres mixing them with untreated linter fibres in different weight ratio. The sheets strength were evaluated using tensile strength. Adsorption of Titanium Dioxide (TiO2) and absorbance of PDDA on the fibers in the solution was measured using the UV Spectrophotometer and Beer Lambert Law. It was shown that the polyelectrolyte treatment increases the strength and double folding of the paper as the weight percentage of the PDDA treated fibers is increased from 0% to 40% and the adsorption of TiO2 on the sheet also increased.  It was also shown that the PDDA treated pulp loses more water in a certain time interval and works as a retention aid for adsorption of TiO2 during the paper sheet formation and change the surface charge to positive. Digital printing technique - copier machine, ink-jet and laser printing - were used the show the advantages of positively charged fiber surface during printing.


Keywords: layer-by-layer nanocoating, retention, digital printing, surface charge
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