The role of surface modification in digital printing on polymer‐coated packaging boards

Digital printing is increasingly being used for package printing. One of the major techniques of digital printing is dry‐toner electrophotography. This paper evaluates the printability of three different extrusion coatings used for packaging boards: low‐density polyethylene (PE‐LD), ethylene methyl acrylate (E/MA) and polyethylene terephthalate (PET). Extrusion coatings in general have an impervious, chemically inert, nonporous surface with low surface energies that cause them to be non‐receptive to bonding with toners. The most common methods used in improving the adhesion properties of polymer coatings are different surface treatments. These increase the surface energy and also provide the polar molecular groups necessary for good bonds between the toner and polymer molecules. The polymer coatings have been modified with electrical corona discharge treatment. The effects of corona on polymer surfaces and the correlation between surface modification and print quality have been evaluated. Results show that sufficiently high surface energy and surface‐charge uniformity are necessary for even print quality and toner adhesion. E/MA and PET have the required surface‐energy level without the corona treatment, but PE‐LD needs surface modification in order to succeed in the electrophotographic process. E/MA also has exceptional surface‐charge properties compared with PET and PE‐LD. Polym. Eng. Sci. 44:2052–2060, 2004. © 2004 Society of Plastics Engineers.