Preventing Mechanical Ink Set off Contamination in Converted Flexible Packaging Web Stock
Prevent mechanical ink set-off in flexible web stock by matching tension taper curves to core pressure limits and verifying cure thresholds.
Polymeric Photoinitiator
Meaning
Light-sensitive chemical compounds with high molecular weights initiate the polymerization of ultraviolet-curable inks and coatings while remaining trapped within the cured matrix. The use of a polymeric photoinitiator minimizes the risk of small molecule migration into packaged goods or the surrounding environment. This specialty additive contains active initiating groups attached to a larger polymer chain backbone.
Molecular Structure
Conventional low molecular weight photoinitiators can easily diffuse through cured film networks because they are not chemically bound to the polymer structure after reaction. This polymeric alternative features multiple benzophenone or thioxanthone groups linked to a polyether or polyester chain. The increased size reduces the mobility of both the unreacted initiator and its photoproducts.
Migration Prevention
Food packaging regulations enforce strict limits on the migration of chemical substances from the printed outer surface of a container to the inner food-contact layer. Utilizing these heavy, multi-functional molecules ensures that the initiating species remain locked within the ink film. This approach eliminates the off-odors and toxicological concerns associated with older ink technologies.
Curing Performance
High viscosity can sometimes limit the mobility of these larger molecules, requiring optimized ultraviolet exposure times to achieve full cure. Adjusting the lamp intensity compensates for the reduced reaction rate.