Precise size control of inkjet-printed droplets on a flexible polymer substrate using plasma surface treatment

The effect of plasma surface treatment on the dried diameter of droplets inkjet-printed on the PI substrate was investigated by varying the plasma process parameters. The sequential design of the experiments technique combining a factorial design with a response surface method was introduced to systematically estimate an accurate empirical response model for two independent design variables: radio frequency (RF) power and gas pressure. C(4)F(8) gas was used for the plasma surface treatment of 90 mm x 90 mm polyimide substrates. Ag ink droplets ejected from a 30 mu m nozzle were printed on the plasma-treated substrates, and their measured diameter and standard deviation were used as the response variables. The plasma-treated substrate was also characterized by contact angles and x-ray photoelectron spectroscopy. The results indicate that the droplet diameters and their uniformity are sensitive to changes in both RF power and gas pressure, lower droplet diameters on PI substrates correspond to lower surface energies, and the process condition producing higher F content results in more hydrophobic surface. The resolution of the inkjet printing can be precisely controlled by varying the droplet diameter and uniformity through the C(4)F(8) plasma surface treatment.