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Effects of the Partial Replacement of SB latex with Dextrin Starch on the Thickness Distribution of Coating Layers
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
2008 (English)In: Tappi 2008 Advanced Coatings Fundementals Symposium Proceedings, Atlanta: Tappi press , 2008, 154-163 p.Conference paper, (Refereed)
Abstract [en]

A pilot coating trial has been carried out where the synthetic binder in the coating colour was partially replaced with dextrin starch. The coating thickness and the coating thickness distribution were investigated by means of burnout tests and mercury porosity measurements. The coating thickness distribution is governed by the surface profile of the base paper underneath the blade; this surface profile is controlled by the compressibility of the base paper and the blade pressure. Dewatering of the coating colours plasticises the paper and increases its compressibility; a linear relationship between dewatering and the standard deviation in the coating thickness was found for a given blade pressure. The characterization of the coating layers showed a small but measurable increase in the thickness variation for increasing starch content, which was caused by the higher water retention of the starch colours. The surface profile of the uncoated and coated paper was investigated with an optical profilometer. The data from those measurements and the coating thickness distribution investigation were used analytically to calculate the roughness change of the base paper during coating. The roughness change was found to be inversely proportional to the original base paper roughness, indicating that the rougher base paper was more compressible.

Place, publisher, year, edition, pages
Atlanta: Tappi press , 2008. 154-163 p.
Keyword [en]
mottling, mass distribution, coating thickness, blade coating, starch, dewatering, surface profiling, compressibility
National Category
Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-14403ISBN: 1-59510-174-8 (print)OAI: oai:DiVA.org:kau-14403DiVA: diva2:542192
Conference
Tappi Advanced Coating Fundamentals, Montreal, Canada
Funder
Swedish Research Council
Note

Part of the thesis: Variations Related to Print Mottle in Starch-Containing Paper Coatings, http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-14409

Available from: 2012-07-30 Created: 2012-07-30 Last updated: 2017-08-14Bibliographically approved
In thesis
1. Variations Related to Print Mottle in Starch-Containing Paper Coatings
Open this publication in new window or tab >>Variations Related to Print Mottle in Starch-Containing Paper Coatings
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Starch in paper coatings is known to increase the risk of print mottle in lithographic offset printing. The objective of this study was to increase the understanding of this behaviour. Four phenomena that could lead to print mottle, where the presence of starch might be important, have been identified: uneven binder migration, uneven coating mass distribution, uneven deformation during calendering and differential shrinkage. The latter three were investigated in this project.

Starch-containing coating colours often have high water retention. A relationship between the water retention of the coating colours and the distribution of coating thickness was found in a pilot trial. A theory is proposed, where the surface profile of the base paper beneath the blade, that governs the coat weight distribution in blade coating, is affected by moisture from the dewatering coating colours and the compressive force exerted by the blade.

Drying strategies were studied to see whether they would induce porosity variations in the coating layers. There is a strong connection between the rate of evaporation and the shrinkage of the coating layer, but no porosity variations due to the choice of drying strategy were found. Shrinkage is governed by the capillary forces. At the same capillary pressure, the coating shrinks more for some binder systems, which is suggested to be due to a weaker chemical interaction between the binder and the pigment.

Oxidized starch/latex coatings, stained with a fluorescent marker, had a greater standard deviation in fluorescence intensity than CMC/latex coatings caused by a difference in either porosity or latex distribution. It was shown that calendering introduces porosity variations into the coating layer that are larger for starch-containing coatings. The drying strategies appeared to have a significant effect on these porosity variations and they correlated positively with print mottle in some cases and in another case negatively. In the case of the negatively correlated, the mottle was probably caused by variations in surface porosity existing prior to the calendering.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2012. 64 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2012:37
Keyword
pigment coating, porosity variations, coating structure, coat weight variations, starch, dextrin, CMC, latex, print mottle, calendering, pilot coating, offset printing
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-14409 (URN)978-91-7063-444-4 (ISBN)
Public defence
2012-09-28, 9C203, Nyquist salen, Karlstad Universitet, Karlstad, 12:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2012-09-11 Created: 2012-07-30 Last updated: 2017-08-14Bibliographically approved

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