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Presentations 2015, 2016

iarigai Toronto 2016
iarigai, VIGC, IS&T at drupa 2016

iarigai VIGC, Brussels
Evolutions in food packaging printing

You are here: Conferences & Events * 2008 Valencia * Abstracts * 4. Color reproduction and quality

4. Color reproduction and quality

4.13. Causes of matt/gloss effects ("ghosting") in sheet-fed offset

Uwe Bertholdt, Gina Sommer

Fogra e.V. Forschungsgesellschaft Druck
Streitfeldstrasse 19
D-81673 München, Germany
E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Abstract
Ghosting in sheet-fed offset printing refers to both matt/gloss effects and back side yellowing. These image defaults are caused by aldehydes liberated during the oxidative ink drying within the printed stack after the print run. The focus of this work is on matt/gloss effects. A laboratory method, which shows a very good predictive ability for production printing, could be developed to reproduce ghost effects. Slower drying inks ghost more strongly. Papers contribute to the occurrence of ghost effects through their influence on the drying speed of the inks. Drying of first side printing inks in the stack results in temporary pre-conditioning of paper sides to be perfected. Trials with paper prepared separately with hexanal demonstrate a correlation between hexanal and the appearance of the ghost effect. Tests about the drying speed of the inks show a faster drying on pre-conditioned paper. The contact phenomena known as ghost effects in sheet-fed offset printing thus result from varying in situ drying speeds of inks.

Keywords: Aldehydes, drying speed, ghosting, laboratory method, matt/gloss effects

 

4.14. Measurement possibilities of interference layers on a paper

Marta Klanjšek Gunde(1), Maša Žveglic(1), Nina Hauptman(1), Gorazd Golob(2)

(1) National Institute of Chemistry
Hajdrihova 19, SI-1000 Ljubljana, Slovenia
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(2) University of Ljubljana, Faculty of natural Sciences and Engineering
Department of Textile, Snežniška 5, SI-1000 Ljubljana, Slovenia

Abstract
Extended interference films can form optically variable devices which are highly important in optical document security area. A layer with similar properties can be deposited also on a paper substrate. We present here that such a layer may show an iridescent colour due to interference of light waves. If the layer is applied on a black substrate, the effect is very clearly seen and can be recorded in reflectance spectrum also by standard measurement geometry applied in printing industry. Much trouble happens on the white substrate where special measurement equipment is needed to measure the interference effect. The optical properties of reflection on such a considerably irregular interference sample are studied and the measurement possibilities to resolve the interference effect are analysed in particular. The possibilities to measure the layer thickness are shown as well.

Keywords: Interference layer, iridescent colour, reflectance measurement

 
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