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Flexographic Ink-Coating Interactions: Effects of Porous Structure Variations of Coated Paperboard
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.ORCID iD: 0000-0001-7368-7227
2013 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 4Article in journal (Refereed) Published
Abstract [en]

Ink transfer and ink penetration into a coated surface, and variations thereof, influences the print density, mottling and dot gain, which affects the achievable print quality and visual appearance. The pressure in the printing nip and the porosity of the substrate are conditions and properties that will regulate the amount of ink that penetrates into a porous coating structure. The purpose of this study was to relate print quality aspects to ink penetration of water-based flexographic ink into calcium carbonate based coatings of differently engineered structures. Pilot-coated paper-boards with different coating porosities were printed in a laboratory flexographic printer. Results indicate that ink transfer distribution is strongly affected by the roughness and the porosity of the substrate. A coating layer of broad pigment particle size distribution resulted in a lower print density, compared to coatings of narrowly distributed particle sizes. A structure characterized by larger pore volume and greater dominating pore radius, showed a higher amount of z-directional ink penetration, which was supported by estimating the penetration using a physical model accounting for both capillary- and pressure driven penetration. A coating with narrow particle size distribution also showed a lower dot gain.

Place, publisher, year, edition, pages
AB Svensk papperstidning , 2013. Vol. 28, no 4
Keyword [en]
Coating, Pigment, Calendering, Porosity, Flexographic Printing, Print quality
National Category
Natural Sciences
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-30026ISI: 000328642400012OAI: oai:DiVA.org:kau-30026DiVA: diva2:664429
Available from: 2013-11-15 Created: 2013-11-15 Last updated: 2015-11-24Bibliographically approved
In thesis
1. Surface and porous structure of pigment coatings: Interactions with flexographic ink and effects on print quality
Open this publication in new window or tab >>Surface and porous structure of pigment coatings: Interactions with flexographic ink and effects on print quality
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Each day, we are confronted with a large amount of more or less important information that we have to consider, and even in our digital society we need paper for communication, documentation and education. Much of the paper we use or are confronted by in our daily life, such as newspapers, books and packages, contains printed images or texts, and the appearance of both the print and the supporting surface is important. A good contrast between a printed text and the paper makes it easier to read, a detailed print of an illustration makes it more informative, and clear and evenly distributed colours on a package or on a poster make it more appealing. All of these qualities depend on the optical properties of the paper product and the the behavior of light illuminating the different materials.

The aim of the work described in this thesis is to characterize the structure of coatings and prints, and to validate models for the optical response and interaction of ink and coating based on optical measurements of physical samples. It is the interactions between the printing ink and the porous structure of the coating layers that are subject to investigation. Experiments have been employed to relate the physical conditions in a flexographic printing nip to the ink setting, affected by the physical and chemical properties of the coating, to the resulting optical response of the printed paperboard.

Abstract [en]

The aim of the work described in this thesis is to characterize the structure of coatings and prints, and to validate models for the optical response and interaction of ink and coating based on optical measurements of physical samples. It is the interactions between the printing ink and the porous structure of the coating layers that are subject to investigation. Experiments have been employed to relate the physical conditions in a flexographic printing nip to the ink setting and the resulting optical response.

By comparing simulated and measured results, it was shown that modifications of the surface properties account for the brightness decrease when substrates are calendered. Light scattering simulations, taking into account the surface micro-roughness and the increase in the effective refractive index, showed that surface modifications accounted for most of the observed brightness decrease, whereas the bulk light scattering and light absorption coefficients were not affected by calendering.

Ink penetration affects the print density, mottling and dot gain. Results show that ink distribution is strongly affected by surface roughness, differences in pore size and pore size distribution. For samples having different latex amounts and different latex particle sizes, a higher print force did not increase the depth of penetrated ink to any great extent, but rather allowed the wetting to act more efficiently with a more evenly distributed ink film, a higher print density and fewer uncovered areas as a result. Uncovered areas could be linked both to local roughness variations and to local wettability variations on the surface. Samples with different ratios of calcium carbonate/kaolin clay pigment showed an increased porosity and an increase in print density with increasing amount of kaolin in the coating layer.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2013. 81 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2013:49
Keyword
Coating, Pigment, Calendering, Porosity, Flexographic Printing, Print quality
National Category
Natural Sciences
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-30030 (URN)978-91-7063-528-1 (ISBN)
Public defence
2013-12-20, Rejmersalen 9C 204, Karlstads universitet, Karlstad, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2013-11-28 Created: 2013-11-15 Last updated: 2013-11-28Bibliographically approved

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