Creasability of novel-coated paperboards for packaging production

Abstract

Driven by sustainability concerns, the use of traditional plastic-based packaging is being questioned owing to its poor degradability and recyclability, and the packaging industry has increasingly reported strong interest in the use of biopolymer dispersion- and extrusion-coated paperboards as substitutes for plastics. However, wider application of these materials is currently limited by convertibility issues in the coated layers, particularly during the processes of creasing and folding. Therefore, this thesis aimed to obtain comprehensive knowledge of the creasability of novel coated paperboards and to improve their convertibility through optimising creasing parameters and developing new tooling to better maintain coating integrity.

Compared with the unconverted state, creasing with industrial tooling induced surface damage in both novel dispersion- and extrusion-coated paperboards; however, the severity of the damage varied depending on the coating type. Alongside negligible surface grazes observed in both coating types after creasing, dispersion coatings exhibited deep surface cracks that significantly impaired their original barrier functionality. Based on the experimental data, the initial surface performance of extrusion coatings was maintained after creasing, without requiring further development. By contrast, the surface properties of the novel dispersions were significantly compromised by creasing, which was addressed by machining the creasing rules from two plastics: polytetrafluoroethylene and polyoxymethylene. The rules produced creases as functional as those formed by a conventional steel rule but preserved surface integrity considerably better, as confirmed by surface microscopy.

This research generates valuable knowledge of the creasability of novel coated paperboards and presents an alternative approach to maintaining their surface integrity after creasing. The creasability was enhanced by reducing friction between the rules and material surfaces, along with optimising creasing parameters such as creasing depth. The results of this study can be used in future research for improving creasability of other coated materials and, on a broader scale, in industrial creasing processes.