Pad printing effectively transfers images onto three-dimensional parts, but adhesion challenges arise with polyethylene and polypropylene substrates due to their low surface energy (measured in dyne levels).
Four pre-treatment options
When standard inks prove insufficient, four pre-treatment options exist: special-formulation inks, chemical wiping, flame treatment, and corona discharge (plasma-jet) systems.
Chemical wiping
Suits prototypes and short runs but introduces workflow complexity and operator exposure.
Flame and corona
For sustained production, flame or corona treatments become necessary, typically integrated into print cells or machinery. Flame treatment offers cost-effectiveness and superior surface preparation for many applications, though some facilities avoid open flames on safety grounds. Corona/plasma systems carry higher purchase costs but work better with certain substrate types.
There is no universal solution
Different PE and PP blends, recycled materials, flame-retardant additives, and colorants all affect adhesion differently. Production decisions depend on throughput requirements, budgetary constraints, and workplace environmental considerations. Testing with ink and equipment suppliers determines optimal approaches for specific applications and material batches.