A Study of water pick-up rates and their effects on ink rheology, ink strength, ink dryback and ink rub-off

Publication Year:
1998
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Abstract Views 39
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Repository URL:
http://scholarworks.rit.edu/theses/3800
Author(s):
Wright, Richard
Tags:
Printing
thesis / dissertation description
It has been thought that the water pick-up rate and capacity of an ink may have a profound affect on the press performance of an ink. As the water content of ink changes so do the Theological characteristics of the ink and this effects ink performance attributes such as ink transfer, drying , rub resistance, set-off and strength. An emulsification curve can shed some light on how ink might perform on a press but this alone is not enough. The objective of this thesis research was to study the interaction of fountain solution and ink as used in the printing of newspapers, in terms of ink water pick-up rates and capacity. Further, this is a study of the effect of the fountain solution and ink interaction on ink transfer, drying, rub resistance, set-off and strength. In this study, three different black news inks and three different fountain solutions have been used to make a total of nine different ink and fountain solution combinations. One set was a specific black news ink and fountain solution combination, Flint Low Rub Black and Anchor Neutral Fountain Solution, used in the printing of USA Today at Boston Offset in Norwood, MA. The paper, a 30# newsprint, was the only newsprint used throughout the testing. Water pick up rates have been determined and emulsification curves have been developed with the use of a Duke Tester for all nine ink and fountain solution combinations. The effect of these water pick-up rates on the rheological characteristics has been studied with the use of a Brookfield Rotational Viscometer. With the use of a motorized Little Joe printability tester, ink was laid down on the newsprint at a constant volume and any changes in ink strength were measured with a densitometer. Rub resistance was examined with a Rub Tester and a densitometer. The experimental data from this study show a direct correlation between the water pick-up capacity of an ink and the affect this has on the ink rheology and ink performance. The tests and data revealed that each ink had a tendency to pick-up more of the alkaline fountain solution than the neutral solution. The least was picked up with the acid fountain solution. The more fountain solution the inks picked up, the greater the changes in viscosity, strength, dryback and rub-off. With the low-rub premium and the dense black, the viscosity rose higher as the ink picked-up more fountain solution. The soy low-rub ink reacted differently. The soy ink had an initial drop in viscosity then, as the ink began to pick up more fountain solution, the viscosity seemed to stabilize. The more fountain solution the ink picked-up the weaker the strength became. At the same time, the more fountain solution that was picked-up, the less density was lost due to dryback and rub-off.