The effect of coating structure on ink-setting and printability
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Helsinki University of Technology |
Diplomityö
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Date
2006
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Paperitekniikka
Mcode
Puu-21
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Language
en
Pages
107
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Abstract
It is well known that ink setting plays an essential role on the final print quality. Ink setting can be re-shaped by coating structure optimization. In this study, the influence of single-coated coating structure with ground calcium carbonate (GCC)-based pigments on offset ink setting is examined using several laboratory approaches, including ink-on-paper tack measurements (ISIT, Deltack and Universal Testprinter), set-off, print gloss and print density development, etc. Some fine-tuning effects together with effects of changing main pigment, GCC, on ink setting are investigated. Both laboratory scale and pilot scale studies are pursued. Conventional broad particle size distribution GCC is seen to retard the long time ink setting rate due to the dense packing, but initial setting can be observably fast. Finer type of narrow particle size distribution GCC mainly increases the capillarity while coarser type seems to generate a more permeable surface. As a result, in both cases the ink-setting rate could be boosted - in the case of the finer pigment at both the initial and final stages, in the case of the coarser pigment at the longer timescales. The presence of platy clay delays ink setting. An increase in the dosage of less platy clay, e.g. secondary high glossing clay, is seen to speed up the ink setting. Binder level affects ink-setting rate. An increase in the dosage of latex can either increase or decrease ink setting rate, depending on its chemistry and physical properties. Smaller-sized latex is demonstrated to slow down the setting rate. The presence of starch is found to be a universally retarding factor for ink setting. Increasing solid content does not appear to change the ink setting performance significantly but improves the surface smoothness in the laboratory trial. While single-variable optimization approaches normally convey a result as expected, including several variables in the recipe optimization does not necessarily deliver a cumulative effect. Set-off is found to chiefly depend on the ink setting rate. Faster ink setting can help to decrease the set-off tendency. Other factors affecting set-off may include the surface topographic properties of the paper, e.g. paper smoothness. Print gloss is found to correlate with the ink property, sheet gloss of the unprinted paper and the ink setting rate. The gloss improvement is more significant for heat-set inks than the sheet-fed ink investigated. Less dense ink seems to require careful control to develop its, often greater, gloss improvement potential. Print density mostly depends on the ink properties, e.g. ink density. Varnish gloss with UV varnish is found to correlate inversely with the permeability of the coating structure and the paper surface characteristics before varnishing. The effect of ink setting on varnishing is better seen as its role on ink film formation on the paper substrate.Description
Supervisor
Paulapuro, HannuThesis advisor
Rennes, SauliKeywords
ground calcium carbonate, coating structure, ink setting, ink-coating interactions, printability