Polyacetal-copolymer (POMB), polycarbonate (PC), polybutylene terephthalate (PBT), and nylon 6, 6 (PA6, 6) have been treated in an electron cyclotron resonance (ECR) plasma chamber to improve their adhesion properties towards ink. The chemical composition, the surface free energy, and the macroscopic adhesion have been studied by X-ray photoelectron spectroscopy (XPS), contact angle measurements, cross-cut tests, and the Scotch Tape test. Their dependence on the neutral gas, the treatment time, the pressure, and the ageing in air have been investigated. The XPS results reveal that the plasma treatment allows one to clean the surface and, if reactive gases are used, to incorporate new chemical species. The static and dynamic contact angles decrease with the plasma treatment and continue to decrease after contact with air. Very slow hydrophobic recovery is visible in the advancing contact angle, whereas the receding contact angle remains non-measurable even after more than a week of air exposure. Lower pressures and longer treatment times (120 s) lead to better macroscopic adhesion and reproducibility. For optimal treatment conditions (0.5 Pa, 120 s N-2 plasma treatment time), the improvement of the adhesion remains excellent after seven days exposure of the sample in air.