The Role of Surface Modification in Digital Printing on Polymer Coated Packaging Boards, 2003 PLACE Conference & GLOBAL HOT MELT Symposium

Packaging is an ideal application for digital printing because of the amount of variable information involved. Digital printing is suitable for short runs of highly personated packages. The obvious benefit of digital printing is the low waste amount and print-on-demand. The status of digital printing, at least in the packaging sector, is still quite moderate, but the future is bright and it has been estimated that the use of this method will increase more than the traditional printing techniques. The quality of digital printing will also approach that of offset.

The aim of this study was to evaluate printability of various extrusion coatings used for packaging boards and to map out the role of surface modification in print quality formation. Extrusion coatings in general have an impervious, chemically inert, non-porous surface with low surface energies that cause them to be non-receptive to bonding with toners. The most common method for obtaining good toner adhesion is to oxidize the surface. This will increase the surface energy and also provide polar molecular groups necessary for good bonds between toner and polymer molecules. The most widely used method to accomplish this is the electrical corona discharge treatment.

In this study, the surface chemistry of the polymer coatings has been modified with the corona treatment. The effects of corona have been evaluated with contact angle measurements and polar powder. Also microscopic methods have been used to analyze the polymer coatings. The influence of surface chemical composition on toner adhesion has been determined by tape-peel and rub-off measurements. Print quality has been analyzed both visually and numerically. Based on these measurements, the correlation between surface properties, toner adhesion and print quality is discussed.