Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Surface and porous structure of pigment coatings: Interactions with flexographic ink and effects on print quality
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
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. , p. 81
Series
Karlstad University Studies, ISSN 1403-8099 ; 2013:49
Keywords [en]
Coating, Pigment, Calendering, Porosity, Flexographic Printing, Print quality
National Category
Natural Sciences
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-30030ISBN: 978-91-7063-528-1 (print)OAI: oai:DiVA.org:kau-30030DiVA, id: diva2:664449
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
List of papers
1. Characterization and modelling of the effect of calendering on coated polyester film
Open this publication in new window or tab >>Characterization and modelling of the effect of calendering on coated polyester film
2009 (English)In: Advances in Printing and Media Technology: Vol XXXVI, 2009, p. 301-308Conference paper, Published paper (Refereed)
Abstract [en]

Polyester films were coated with a coating colour based on a ground calcium carbonate with narrow particle size distribution. Four different coat weights were produced. The coated sheets were calendered and the samples were exposed to up to twenty nips in the calender at a line load of 300 kN/m at 50°C. The brightness and the thickness were measured after each calendering nip. Reflectometry was used to measure the refractive index and the microroughness of the samples. Calendering lead to a decrease of the Kubelka-Munk scattering coefficient and an increase of the absorption coefficient of the coated transparent films. Taking into account non-uniform surface reflection at the boundaries between media of different refractive indices, a large part of the reflectance decrease due to calendering could be attributed to an increase of the effective refractive index at the coating surface and a decrease of the surface microroughness.

Keywords
Coating, Calendering, Gloss, Brightness, Refractive index
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-6828 (URN)978-3-9812704-1-0 (ISBN)
Conference
Proceedings of the 36th International Research Conference of airigai, Stockholm, Sweden, 2009
Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2014-10-27Bibliographically approved
2. Modelling of Brightness Decrease of Coated Cartonboard as an Effect on Calendering: Microroughness and Effective Refractive Index Aspects
Open this publication in new window or tab >>Modelling of Brightness Decrease of Coated Cartonboard as an Effect on Calendering: Microroughness and Effective Refractive Index Aspects
2010 (English)In: TAPPI 11th Advanced Coating Fundamentals Symposium, Munich, Germany, 2010: Symposium Proceedings, Norcross, GA, USA: TAPPI Press, 2010, p. 51-65Conference paper, Published paper (Refereed)
Abstract [en]

Calendering of coated paper leads to a brightness decrease. The mechanism for this is not clear, although it has been discussed in the past. One common explanation is that the porosity of the coating layer decreases and hence scattering. By comparing simulated and measured results this paper shows that modifications of the surface properties account for the brightness decrease of GCC coated substrates with calendering. The effect of a deformable cartonboard substrate is investigated here and compared to a less deformable plastic film substrate. From simulations based on a two-layer Kubelka-Munk model, it is shown that the brightness decrease of the cartonboard due to calendering has a negligible contribution to the brightness decrease of the coated cartonboard. The brightness decrease was similar for coated plastic film and coated cartonboard. The thickness of GCC coated plastic films was not affected by calendering irrespectively of the pigment and latex size distribution. Monte Carlo light scattering simulations, taking into account the measured decrease of surface microroughness and increased effective refractive index, showed that surface modifications accounted for most of the observed brightness decrease of the GCC coated substrate, whereas the bulk scattering and absorption coefficients were not affected by calendering. It is also shown that the scattering coefficient is significantly dependent on the coat weight whereas the physical absorption coefficient is not.

Place, publisher, year, edition, pages
Norcross, GA, USA: TAPPI Press, 2010
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-6830 (URN)1-59510-203-5 (ISBN)
Conference
TAPPI 11th Advanced Coating Fundamentals Symposium, Munich, Germany, 11-13 October 2010
Available from: 2011-01-27 Created: 2011-01-27 Last updated: 2014-10-27Bibliographically approved
3. Flexographic Ink-Coating Interactions: Effects of Porous Structure Variations of Coated Paperboard
Open this publication in new window or tab >>Flexographic Ink-Coating Interactions: Effects of Porous Structure Variations of Coated Paperboard
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
Keywords
Coating, Pigment, Calendering, Porosity, Flexographic Printing, Print quality
National Category
Natural Sciences
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-30026 (URN)000328642400012 ()
Available from: 2013-11-15 Created: 2013-11-15 Last updated: 2017-12-06Bibliographically approved
4. Flexographic ink-coating interactions: Effects of latex variations in coating layers
Open this publication in new window or tab >>Flexographic ink-coating interactions: Effects of latex variations in coating layers
2016 (English)In: TAPPI Journal, ISSN 0734-1415, Vol. 15, no 4, p. 253-262Article in journal (Refereed) Published
Place, publisher, year, edition, pages
TAPPI Press, 2016
National Category
Chemical Sciences
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-30027 (URN)000382526700003 ()
Available from: 2013-11-15 Created: 2013-11-15 Last updated: 2017-12-06Bibliographically approved
5. Flexographic ink-coating interactions: Effects of kaolin clay/GCC blends in coating layers
Open this publication in new window or tab >>Flexographic ink-coating interactions: Effects of kaolin clay/GCC blends in coating layers
(English)Manuscript (preprint) (Other academic)
Keywords
Printing Flexography Kaolin GCC
National Category
Natural Sciences
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-30025 (URN)
Available from: 2013-11-15 Created: 2013-11-15 Last updated: 2016-11-22Bibliographically approved

Open Access in DiVA

Surface and porous structure of pigment coatings(2380 kB)1700 downloads
File information
File name FULLTEXT01.pdfFile size 2380 kBChecksum SHA-512
92654463a26cb36f244283964d34d2b72aebcd63278ab50145ee27bec476b1393dcce998b2f83e6455750531070da18c1fcb84fbc9f4a7697cb29503a62185a6
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Bohlin, Erik
By organisation
Department of Engineering and Chemical Sciences
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 1700 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 700 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf