Printing Ink Set-off

Transfer Mechanism

When printed sheets are compressed in high stacks, the pressure forces the partially cured ink into direct contact with the unprinted plastic surface. Insufficient curing leaves the ink tackier and more prone to adhesive failure at the ink polymer interface. This issue is common in fast flexographic printing lines where the web speed exceeds the capacity of the drying ovens.

Increasing the oven temperature or utilizing ultraviolet curing systems accelerates the ink drying and prevents this physical transfer from taking place.

Material Factor

Surface energy of the polymer substrate determines how well the ink adheres and how quickly it dries. Corona treatment increases the surface energy of polyethylene and polypropylene, which promotes robust chemical bonding and limits ink mobility. In contrast, low surface energy substrates prevent proper wetting and lead to localized ink pooling that resists complete drying.

Moulding additives such as slip agents or antistatic chemicals can migrate to the surface of the part and interfere with ink curing, causing severe transfer issues.

Prevention Strategy

Packaging operations manage this risk by incorporating anti set-off powders or anti blocking agents into the polymer resin or surface coating. These additives create microscale surface roughness that reduces the contact area between the stacked sheets. Implementing in line optical detection systems allows operators to monitor ink dry times and adjust process variables before the material enters the stacking phase.

Regular tape tests on cured ink samples provide a simple method to verify adhesion strength and prevent scrap in downstream assembly.