Kaisa Koivumäki, Erkki K. O. Hellén

Abstract
Drying dynamics was studied by extensive measurements on a full-scale heatset web offset press. The most important parameters influencing on drying are dryer air temperature, temperature profile and ink amount. For coated papers also the coat weight has a significant effect. Unexpectedly, considerable amount of solvent evaporates simultaneously with moisture at the early stages of drying. For normal drying conditions, some solvent and moisture remain in paper structure. Physical modeling was used to help in interpreting the experimental observations and in seeking for deeper understanding of the underlying drying mechanisms.

Keywords: Heatset printing, Drying, Solvent evaporation, Moisture evaporation, Residual solvent, Modeling
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Gorazd Golob, Miran Mozetič, Kristina Eleršič, Ita Junkar, Dejana Đorđević, Mladen Lovreček

Abstract
The goal of investigation was to determine surface free energy, roughness and other properties of NBR and EPDM rubber blankets, modification of the surface properties using oxygen plasma treatment and defunctionalization of the surface. Characterization of the surface free energy by contact angle measurements using different disperse and polar liquids, SEM and roughness analysis of the investigated untreated and plasma treated elastomers gives a quantitative description of achieved surface modifications. Plasma treated rubber blankets achieved higher surface free energy and have become more hydrophilic but a superhydrophilic stage with contact angle with water near 0º was not achieved during the investigation. Contact angle with water remained almost unchanged after 24 hours. Roughness of treated surface has arisen. There were no significant differences between NBR and EPDM rubber blankets.

Keywords: EPDM rubber blanket, NBR rubber blanket, Oxygen plasma, Surface free energy
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Tim C. Claypole, Georgios Vlachopoulos, David C. Bould

Abstract
Ink film splitting in flooded nips of non Newtonian fluids is core process physics of the inking train of the offset litho press. Understanding the interactions of the ink and the dynamics of the fluid flow to the printing plate is key to improving press design and also eliminating problems such as inconsistency, ghosting and misting. The splitting mechanism gives rise to local variations in the ink film thickness. In coating, where there is no oscillation of the rolls across the direction of print, this can lead to the development of discrete ribs of ink across the width of the roller.

A printability tester was used to recreate the conditions in a rolling nip contact and operated in such a manner as to enable the study of film splitting instabilities. The method of operation and measurement techniques use to study the ribbing phenomenon are described as well as preliminary measurements undertaken to evaluate the technique.

Ribbing was found to be primarily generated due to elongation mechanism at the nip exit, where ink is deformed in filaments and splits. The rotation rates do not allow ink to recover its elasticity or redistribute itself before the next time it is split. The film thickness, viscosity and speed were found to have the most effect on ribbing both the frequency and width of the ribs.

Keywords: Offset, Ink transfer, Film splitting, Instabilities
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