Why does ink fail to adhere to plastic parts?

Record what changed before adjusting settings

A polymer name does not fully describe a printable surface. Resin grade, additives, pigments, release agents and storage history can influence how an ink behaves. Parts that look clean can still carry a thin contaminating layer. Lubricants or other additives may migrate toward the surface after molding.

Compare a failing sample with an accepted sample made under known conditions. Record material lot, relevant cavity information, product age, treatment settings, ink batch and the time between treatment, printing and testing. This makes it possible to investigate the source of variation instead of changing several parameters at once.

Separate wetting from the finished bond

Wetting describes how a liquid spreads on a solid. Adhesion describes the attachment of the printed layer to the substrate or to another ink layer. Surface activation may improve wetting, but the final result also depends on chemical compatibility, contamination, ink-film integrity and curing.

Dyne testing provides a practical indication of wetting behavior. It does not measure adhesion strength. Curvature, contamination and the observation method affect its interpretation. Contact-angle measurement offers another view of the surface, although its result also depends on the liquids, geometry and method used.

Use the failure pattern to choose the next check

The checks below are starting points for investigation. They do not identify a cause without testing. Keep the other conditions controlled while assessing a suspected variable.

Verify the result after the relevant exposure

Select adhesion and durability tests from the product requirements, and define the time after printing at which they will be performed. A freshly printed sample and a fully conditioned sample can behave differently. Include relevant rubbing, chemical exposure or downstream processing where those conditions form part of the intended use.

AAE evaluates print appearance, adhesion and dimensional requirements during print development. Share the failed parts, accepted reference parts and the test specification so the investigation can address the actual production problem.