Experimental investigations into fold cracking of double coated barrier dispersion coatings, TAPPI Journal November 2024

Application: This work continues to build on previous work that has shown some benefits in barrier performance by including minerals, due to a longer tortuous path for the oil or water vapor to move around. However, we found that it was not just important to look at the sheet as coated before folding or creasing. The process of converting puts additional strain on the sample, and we found that a moderately platy kaolin outperformed an extremely platy one after the folding was carried out and the barrier properties assessed. Therefore, the converting step should also be considered during the formulation development. This work should help guide development teams in their choice of mineral if it is added, as well as a suitable amount.

Author: Janet Preston, Gavin Butler-Lee, Chris Nutbeem, and Chris Disberry

ABSTRACT: The trend for replacing single-use plastics with fiber-based barrier coated board packaging has prompted a significant amount of research. There are many proposed ways of providing suitable packaging for applications like food service. Among these are dispersion coated barriers on board, as well as laminated boards that can be produced using conventional polyethylene (PE) or new biodegradable plastics. Minerals have also been shown to be suitable additives to these coatings for improving barrier performance through surface chemistry and by increasing the tortuosity of the pathway through the barrier layer. They also improve the cost effectiveness of the layer by lowering the material cost and raising the solids content, and by improving hold out of the functional layers, leading to a reduction in the amount of barrier coating needed to meet a given performance requirement. Minerals can also aid in the barrier handling in terms of rheology and reduced “stickiness,” as well as blocking of the films. When incorporated as fillers into extruded films, improved adhesion of the film to the board has been reported. One of the remaining challenges is the potential for cracking at the fold during converting and the loss of barrier performance that this can lead to. In this work, we systematically looked at the impact of mineral type and level in a dispersion coating. We assessed the differences in performance resulting from different coating application methods for the precoat layer by looking at the cracking tendency and loss of barrier functionality after folding for both the precoat alone and the final double coated sheets. Barrier results include moisture vapor transmission rate (MVTR), viscous vegetable oil, and the fluid blue stain in industrial methylated spirits (IMS) and Cobb water absorption, both before and after folding.