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Effect of excess dispersant on surface properties and liquid interactions on calcium carbonate containing coatings
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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2010 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 25, no 1, 82-92 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this work was to identify what effects excess amount of sodium polyacrylate, a commonly used dispersant, has on the coating properties and the interaction between ink and the paper coating in offset printing. Since polyacrylate strongly interacts with calcium ions, soluble calcium salt was added to some coating colours to illustrate the impact of charge neutralization by calcium ions. It was found that the coating structure was only slightly affected by the extra addition of polyacrylate, showing some weak flocculation, whereas the surface chemistry was strongly influenced. The coatings became more polar and interacted more strongly with water. This resulted in slower ink setting and reduced ink-paper coating adhesion, especially in the presence of applied water/dampening solution, which are identified as contributory factors in ink piling and print mottle.

Place, publisher, year, edition, pages
2010. Vol. 25, no 1, 82-92 p.
Keyword [en]
Coating, Sodium polyacrylate, Hygroscopy, Offset, Ink-paper coating interaction, Coating structure, Surface energy, Ink adhesion
National Category
Paper, Pulp and Fiber Technology
URN: urn:nbn:se:kth:diva-27570DOI: 10.3183/NPPRJ-2010-25-01-p082-092ISI: 000278043500011ScopusID: 2-s2.0-78650715032OAI: diva2:377893

QC 20101215

Available from: 2010-12-15 Created: 2010-12-13 Last updated: 2016-10-19Bibliographically approved
In thesis
1. Interfacial Adhesion Failure: Impact on print-coating surface defects
Open this publication in new window or tab >>Interfacial Adhesion Failure: Impact on print-coating surface defects
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this work was to develop a solid knowledge on formulation effects controlling offset ink-paper coating adhesion and to identify key factors of the coating and printing process affecting it. Focus lay on comprehending the impact of pigment dispersant on ink-paper coating adhesion and ultimately on the print quality of offset prints.

The work covers laboratory studies, a pilot coating trial designed to produce coated material with a span in surface chemistry and structure, and an industrial offset printing trial.

The lab scale studies quantified ink-paper coating adhesion failure during ink setting with a developed laboratory procedure based on the Ink-Surface Interaction Tester (ISIT) and image analysis. Additional polyacrylate dispersant resulted in slower ink setting and reduced ink-paper coating adhesion, with a dependence on its state of salt neutralisation and cation exchange, mainly in the presence of moisture/liquid water.

The industrial printing trial on pilot coated papers was designed to study how these laboratory findings affected full scale offset print quality. These trials confirmed the dispersant-sensitive effect on ink-paper coating adhesion, especially at high water feeds. Evaluation of prints from the printing trial resulted in two fundamentally different types of ink adhesion failure being identified. The first type being traditional ink refusal, and the second type being a novel mechanism referred to as ink-lift-off adhesion failure. Ink-lift-off adhesion failure occurs when ink is initially deposited on the paper but then lifted off in a subsequent print unit. In this work, ink adhesion failure by this ink-lift-off mechanism was observed to occur more often than failure due to ink refusal.

Print quality evaluation of the industrial prints suggested that water induced mottle was caused by a combination of ink-surface adhesion failure, creating white spots on the print, together with variation in ink layer thickness due to emulsified ink.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 102 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2016:35
Ink-paper coating adhesion, offset printing, calcium carbonate pigments, polyacrylate, dispersant, print mottle, surface chemistry, hygroscopy of surfaces, coating structure, print quality, water interference mottle
National Category
Chemical Engineering
Research subject
Fibre and Polymer Science
urn:nbn:se:kth:diva-194166 (URN)978-91-7729-136-7 (ISBN)
Public defence
2016-11-18, F3, Lindstedtsvägen 26, Stockholm, 09:00 (English)

QC 20161019

Available from: 2016-10-19 Created: 2016-10-18 Last updated: 2016-10-19Bibliographically approved

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