Definitional Property
Surface properties determine the ability of a coated substrate to resist sticking to itself when stored under pressure or heat. Achieving high block resistance prevents the unintended adhesion of stacked sheets or wound rolls in a warehouse environment. It is a metric for labels and flexible packaging where ink surfaces contact the reverse side of the material.
Testing Methodology
Laboratory assessment involves placing two printed surfaces together under a defined weight for a specific duration and temperature. The block resistance is then rated based on the force required to separate the layers and the amount of surface damage observed. If the coating fails, the resulting picking or tearing destroys the visual integrity of the package.
Formulation Influence
The glass transition temperature of the polymer binders and the inclusion of anti-blocking agents like waxes or silicas directly impact this performance. While soft resins might offer better flexibility, they often reduce block resistance by becoming tacky at elevated temperatures. Careful selection of hard particles provides a microscopic physical barrier that keeps the film surfaces apart.
This mechanical separation reduces the contact area between the polymer chains of the opposing layers. High humidity levels can exacerbate blocking issues in water based systems by plasticizing the coating layer.
