Polyolefine plastics. Sheets or molded matters are often used as the substrates. They are difficult materials to adhere. As ink does not adhere to untreated materials, it is essential to treat the surface before print. The treatments are corona discharge, flame or primer-coating.
Polyacetal is the most difficult material in polyolefin plastics. Baking is necessary as well as pre-treatment to obtain good adhesion.