A new method of blocking quantification for coated paperboard

摘要

Blocking is defined as undesired adhesion between two surfaces when subjected to pressure and temperature constraints. Blocking between two coated paperboards in contact with each other may be caused by inter diffusion, adsorption and/or electrostatic forces occurring between the respective coating surfaces. These interactions are influenced by external factors such as the temperature, pressure, surface roughness and surface energy but to name a few. Blocking can hence be potentially reduced by tuning these factors. Another way to reduce blocking is to use antiblocking additives such as talc, amorphous silica, fatty acid amides or polymeric waxes. A short review is given on the principle of blocking and the antiblocking additives operate. The method of quantifying blocking presented was developed using an Anton Paar MCR-501 Rheometer. Coated surfaces were put in contact with each other with controlled pressure and temperature for a definite amount of time. The two surfaces were then separated from each other while measuring the normal force necessary to pull them apart from each other. The maximum normal force measured immediately before the two surfaces detached from each other, referred to as the "blocking force", was found to be a reproducible way to accurately quantify blocking. Illustratively, this method was applied to the determination of the impact external factors have on the blocking tendency of coated paperboards, i.e. antiblocking additive concentration, film thickness, temperature and humidity.