Extrusion coating of dense specialty papers

The packaging industry is actively seeking for innovative and recyclable paper-based packaging materials. Coating of greaseproof papers has been shown to provide materials, for example, with a good oxygen barrier. However, obtaining a good adhesion can be a challenge in extrusion coating, especially with smooth papers. Our objective was to shed light on these phenomena by extrusion coating different dense specialty papers with two different polymers (low density polyethylene and biopolymer).

Good adhesion was obtained with a corona pretreatment and by optimizing other process parameters. However, with the biopolymer achieving good adhesion was more challenging than with the polyethylene. In addition, the criteria of adhesion based on fiber tear with standard papers is not necessarily valid with specialty papers.

The base paper had a significant impact on oxygen barrier, but a good interfacial contact between the paper and the polymer layer is required to maximize the barrier potential. The best barrier was achieved with substrates having a low surface porosity or some barrier already without the coating. Increasing humidity decreased barrier emphasizing the role of the base paper.