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  • 1.
    Bohlin, Erik
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Optics of coated paperboard: Aspects of surface treatment on porous structures2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Calendering of coated and uncoated paper is widely used to enhance optical properties such as gloss and print quality. The aim of this thesis is to characterize coatings and prints, and to validate models using experimental results from optical measurements of physical samples.

    Calendering of coated paper often leads to a brightness decrease. The mechanism for this is not altogether clear. One common explanation is that the porosity of the coating layer decreases and hence the scattering decreases. By comparing simulated and measured results it was shown that modifications of the surface properties account for the brightness decrease of ground calcium carbonate coated substrates with calendering. 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 ground calcium carbonate coated substrate, whereas the bulk scattering and absorption coefficients were not affected by calendering. It was also shown that the scattering coefficient is significantly dependent on the coat weight whereas the physical absorption coefficient is not.

    The penetration of ink in the z-direction of a substrate influences the quality of the print. The ink penetration affects print density, mottling and dot gain, common print effects that influence the preference of consumers. The pressure in the printing nip and the porosity of the substrate both affect the amount of ink that is pressed into the porous structure of a coating layer during printing. By printing pilot coated paperboard with different coating porosity and measuring the resulting optical properties of the prints, a basis for simulations of the different layers, that is to say the coating, the print and the mixed layer in between, was created. Results show that ink distribution is strongly affected by the roughness of the substrate. Fibres and fibre flocks underneath the two coating layers created an unevenly distributed coating thickness that affected the print quality. Differences in pore size and pore size distribution also affected the behaviour of the ink. A coating layer of broad pigment particle size distribution resulted in a relatively low print density, in comparison to coatings of narrowly distributed particle sizes. Comparison of dot gain showed that the coating layer of a narrow particle size distribution had a relatively low dot gain compared to others. In this work, these results are explained by the differences in ink distributions on and in the coating layers.

  • 2.
    Bohlin, Erik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Surface and porous structure of pigment coatings: Interactions with flexographic ink and effects on print quality2013Doctoral 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.

  • 3.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Coppel, Ludovic
    Innventia AB, Stockholm, Sweden.
    Andersson, Caisa
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Edström, Per
    Mid Sweden University.
    Characterization and modelling of the effect of calendering on coated polyester film2009In: Advances in Printing and Media Technology: Vol XXXVI, 2009, p. 301-308Conference 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.

  • 4.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Coppel, Ludovic
    Innventia AB, Stockholm, Sweden.
    Johansson, Caisa
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Edström, Per
    Mid Sweden University.
    Modelling of Brightness Decrease of Coated Cartonboard as an Effect on Calendering: Microroughness and Effective Refractive Index Aspects2010In: TAPPI 11th Advanced Coating Fundamentals Symposium, Munich, Germany, 2010: Symposium Proceedings, Norcross, GA, USA: TAPPI Press, 2010, p. 51-65Conference 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.

  • 5.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
    Johansson, Caisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
    Lestelius, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
    Evaluation of ink penetration in porous coatings2012Conference paper (Refereed)
  • 6.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Johansson, Caisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Lestelius, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Flexographic ink-coating interactions: Effects of kaolin clay/GCC blends in coating layersManuscript (preprint) (Other academic)
  • 7.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
    Johansson, Caisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
    Lestelius, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences, Paper Surface Centre.
    Flexographic ink-coating interactions: effects of kaolin clay/GCCblends in coating layers2014Conference paper (Refereed)
  • 8.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Johansson, Caisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Lestelius, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Flexographic ink-coating interactions: Effects of latex variations in coating layers2016In: TAPPI Journal, ISSN 0734-1415, Vol. 15, no 4, p. 253-262Article in journal (Refereed)
  • 9.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Johansson, Caisa
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Lestelius, Magnus
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Flexographic Ink-Coating Interactions, Effects of Porous Structure Variation of Coated Paperboard2012Conference paper (Refereed)
  • 10.
    Bohlin, Erik
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Lestelius, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Johansson, Caisa
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
    Flexographic Ink-Coating Interactions: Effects of Porous Structure Variations of Coated Paperboard2013In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 28, no 4Article in journal (Refereed)
    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.

  • 11.
    Johansson, Caisa
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre.
    Bohlin, Erik
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Surface characterization and model verification2009Conference paper (Other (popular science, discussion, etc.))
  • 12.
    Johansson, Caisa
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Paper Surface Centre.
    Bohlin, Erik
    Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering. Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
    Coppel, Ludovic
    Edström, Per
    Modelling of coating brightness: Impact of micro-roughness and effective refractive index2011Conference paper (Other (popular science, discussion, etc.))
  • 13.
    Johansson, Caisa
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Bohlin, Erik
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Lestelius, Magnus
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
    Impact of coating composition and structure on print quality of flexographic printed paperboard2016In: 14th TAPPI Advanced coating symposium proceedings, Peachtree Corners, GA: TAPPI Press, 2016, p. 14-17Conference paper (Other academic)
1 - 13 of 13
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  • en-US
  • fi-FI
  • nn-NO
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