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Paper Coating Properties as Affected by Pigment Blending and Calendering: An Experimental Study
Karlstad University, Faculty of Technology and Science, Department of Chemical Engineering.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Paper Surface Centre.
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2005 (English)Conference paper, Published paper (Other (popular science, discussion, etc.))
Abstract [en]

Many end-use properties of coated papers can be improved by optimizing coating formula-tions, more specifically by selecting and/or blending different types of pigments and binders. Although clay and GCC, with very different particle shapes, are known to create different coating structure, it is not well understood how and why blending these pigments affects the micro-structure. In addition, since most of the coated papers are subjected to calendering, it is also important to know to which extent the structures created by pigment blending are compressed by calendering. The aim of this work was, therefore, to gain insights into how and why pigment blending affects coating pore and surface structure, before and after cal-endering. Coating colours with different blending ratios of GCC and clay were prepared with a constant level of binder and co-binder. The coatings (30 g/m2) were then applied on plastic films and calendered using a paper sheet backing beneath to account for the part of com-pression absorbed by the base paper. Mercury porosimetry was used to characterize the pore structure of the coatings, while an AFM and an interference microscope were used to characterize the surface structure at a pigment size level. The results obtained from these techniques were also compared with and complemented by measurements of gloss and op-tical properties. The results showed that synergy occurs for various coating properties when blending GCC and clay. For example, the pore volume and pore size reached a maximum value around 70% clay and 30% GCC. This confirms the predictions obtained from particle packing simulation. Synergistic effect was also observed on light scattering which is con-trolled by the coating pore structure. However, no synergy was observed for smoothness and gloss. The gloss actually reached a minimum at low clay content and this was attributed to disordering of GCC structure by clay plates. It was found that calendering significantly compressed the coating layers (up to 45% decrease in pore volume), and some of the syn-ergies created by the blending were lost after calendering. Although the pure clay coating was twice more compressed by the calendering than the pure GCC coating, the blending of clay and GCC at a wide range of ratios showed a similar extent of compression. A mecha-nism is proposed to explain the observed synergies by blending and the compression caused by calendering

Place, publisher, year, edition, pages
2005.
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-22231OAI: oai:DiVA.org:kau-22231DiVA, id: diva2:595908
Conference
22nd PTS Coating Symposium, September 20-22, Baden-Baden, Germany (2005)
Projects
Consolidation of Coating LayersAvailable from: 2013-01-21 Created: 2013-01-21 Last updated: 2013-01-21

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Larsson, MikaelEngström, Gunnar

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