Ink‐Coating Adhesion: The Importance of Pore Size and Pigment Surface Chemistry

Abstract

The characteristics of ink vehicle absorption into porous structures has formed the basis of a number of recent studies. Kalela, Ridgway and Gane (11th International Printing and Graphic Arts Conference, Bordeaux, 2002) considered an example of common impression cylinder deposits as a result of poor coldset ink adhesion especially in the presence of excess fountain solution. These studies centre on the absorption mechanisms of pigmented coatings and how these can be adjusted to enhance ink‐coating adhesion. By developing techniques of tack cycle analysis and correlation with adhesion, i.e. observing print density on the pull‐off areas using the ink‐surface interaction tester (ISIT), it has been possible to assess ink‐coating adhesion. To enhance the adhesion properties of inks, two strategies for coating designs are discussed. The first is to increase the number of ultrafine pores and to increase simultaneously the pigment surface area to enable a capillary‐driven separation of oils from solved resins and to provide higher adsorptive power for resins. This was tested by the inclusion of a novel surface‐structured calcium carbonate. The second is to introduce an oleophilic species into the coating structure, achieved by the inclusion of hydrophobic talc via a co‐structure between talc and hydrophilic dispersed calcium carbonate (Gane, Buri, and Blum, International Symposium on Paper Coating Coverage, Finland 1999). Mercury porosimetry measurements of model coatings using these pigment combinations are used to illustrate their effect on coating structure. These structures are modelled using a computer network simulator, an absorption algorithm is applied to generate the absorption dynamic for each structure. The differences in wetting front are illustrated. It is seen that only at the shortest timescales is there any difference in the absorption dynamic (ignoring any surface chemistry effects). It can therefore be concluded that the observed improvements in this study of ink adhesion are related to adsorptive mechanisms, and absorption rate governs the dwell time over which this adsorption can occur.

Keywords:

• Ink tack
• Ink adhesion
• Printability
• Ink absorption
• Ink setting

Notes

^aISIT is a product name of SeGan Ltd., Perrose, Lostwithiel, Cornwall PL22 0JJ, UK.

^bPore‐Cor is a software product name of the Environmental and Fluids Modelling Group, University of Plymouth PL4 8AA, UK.

^cMethod used by Deltack: a product name of Prüfbau Print Testing Equipment.

^dSynteape is a product name of Arjo Wiggins, Cedex, France.

^eSetacarb is a product name of Omya AG, CH 4665 Oftringen, Switzerland.

^fAcronal is a product name of BASF, Ludwigshafen, Germany.

^gIt forms just one of a family of newly developed surface modified pigments of various particle size and surface area.

^hPore‐Comp is a software program developed by the Environmental and Fluids Modelling Group, University of Plymouth, PL4 8AA, UK.