Study of Rheology and Adhesion in Extrusion Coating of Different Polyethylenes, 1998 Polymers, Laminations & Coatings Conference Proceedings

The target was to compare more or less linear polyethylenes (PE-HD and PE-LLD) and branched low-density polyethylenes (PE-LD) in extrusion coating. Adhesion, water vapor barrier and rheological properties were studied. Rheological properties, in this context, include draw down and neck-in in extrusion coating and rheological determinations with a slit-die rheometer. Rheological parameters, such as viscosity and Power law constant n, were determined at the same temperatures (295 and 3 15’C) as the resin melt temperatures in the extrusion coating experiments.

The results indicate that the used linear polymers PE-HD and PE-LLD provided much broader neck-in and higher viscosity than the three LD-polyethylenes. Clearly, linear PE-LLD and PE-HD showed much greater draw ratios than branched LD-polyethylenes. This enables faster line speeds with thinner coatings.

Both corona and corona + ozone pretreatments improved substantially adhesion between PE and paper. The improvement of corona is more pronounced at higher (315°C) temperatures whereas the ozone promotes adhesion best at lower (295°C) temperatures. These results are caused by the oxidation of the polymer films.