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Evolutions in food packaging printing

You are here: Conferences & Events * 2010 Montreal * Abstracts * 2. Improving print quality

2. Improving print quality

2.04 Quality and efficiency enhancement in heatset web-offset drying by adopting thermally designed paper coatings

Philip Gerstner, Teemu Grönblom, Patrick A. C. Gane

Abstract
For print quality and efficiency out of the drying section in heatset web-offset (HSWO) printing, the four components of dryer design/setting, substrate, inks and fountain solution play a combined role. This work analyses the effect of coated substrate, particularly the impact of the coating layer design, on print quality parameters like printed gloss, roughness and waviness. Since waviness is to a certain degree due to an uneven moisture profile, it is investigated how thermal barrier coatings might be used to reduce the waving (fluting) tendency by shielding the basepaper from the heat of the dryer. Two thermally insulating paper coating constructions are formed using precoatings consisting of either platy mica or a blend containing a highly porous modified calcium carbonate (MCC). Both coating concepts have a comparable topcoating formulation applied and are compared to two references, one consisting of a double coating 100 % calcium carbonate formulation concept and the second a single coating of comparable coat weight based on a typical commercial calcium carbonate-rich coating formulation. The mica precoated paper was shown to exhibit lowest waving tendency. The mica precoating can reduce waving effects even more effectively at high moisture contents and high drying temperatures. By studying the liquid permeability of the mica layer, it is found that the tortuous precoating layer formed by the mica platelets acts to combine a liquid and thermal barrier, such that both quality and efficiency enhancements, due to reduced fountain solution and ink vehicle permeation, can be achieved. However, the lower brightness of the mica pigment studied, compared to calcium carbonate pigments remains a drawback in practice.

Keywords: heatset web-offset, drying, energy efficiency, waving, fluting, blistering, thermal properties, printability
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2.05 A laboratory method to characterize and predict ink misting

Saeid Savarman, Douglas Bousfield, Richard R. Durand Jr., Bob Warren

Abstract
Misting is a common issue for high speed offset press operation. A laboratory device is used to characterize misting. Computer controlled drives turn rolls at known speeds. A flush mounted pressure transducer is used to record the pressure distribution during operation. Plastic strips, placed under the nip, capture mist generated. Several inks were characterized with a stress-controlled rheometer. Proposed dimensionless numbers consolidate the results for the inks studies in this work. A model of fluid slinging from a roll is proposed. The amount of misting inversely correlates with the pressure peak generated in the nip and directly increases with increasing the Reynolds number. The slinging model predicts that centrifugal forces can pull fluid into defects to enlarge filaments that can lead to slinging, but this mechanism only explains the results at high speeds. Misting at low speeds must come from a filament breakup pattern driven by surface tension.

Keywords: misting, filaments, rheology
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2.06 Evaluation of gray balance and G7 in inkjet proofing of GRACoL and SWOP printing

Martin Habekost, Rebecca Dykopf

Abstract
The printing industry uses inkjet proofing systems to match and predict the result of offset printing. Most often when generating proofs these results are represented by GRACoL, SWOP#3 and SWOP#5 reference printing conditions. Traditionally, the measure of how well a system matches an offset reference printing condition is based on a Delta E measure, averaged over measurements of an IT8.7/4 test target (1617 patches). This research seeks to determine if the new IDEAlliance ISO 12647-7 Digital Control Strip 2009, with only 54 patches can provide the same or similar verification, for everyday, practical situations. Another variable in offset printing and inkjet proofing is G7 gray balance. The G7 process is being implemented by many printers in the North American print industry. This research seeks to measure G7 gray balance in inkjet proofs and analyze the relationship between G7 and match to a reference printing condition as calculated by measuring the IT8.7/4 target. The data for this study was gathered as part of the IPA Technical Conference in 2009, and considers 21 proofs from 8 different suppliers, as well as 32 proofs from the end user community.

Keywords: inkjet proofing, gray balance, GRACoL, SWOP, G7, ISO 12647
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