Examination of gravure printed films for polymer light emitting devices: Master's thesis

The structure and function of a low information-content PLED were examined and the focus was on the gravure printed structures as well as on the gravure printing process. The layers of the device are required to be extremely thin, smooth and no pinholes are allowed. Therefore, it is important to understand the gravure printing process in order to achieve sufficient product quality and reproducible production. The orange-emitting MEH-PPV-POSS layers were fabricated with gravure printing and both the layer thickness and roughness were examined. The operation of the gravure printing process was evaluated. The factors most affecting the printing process and the responses regarded as the most significant were evaluated. Experiments were carried out with the help of a systematic experimental design. The software Modde 6.0 (Umetrics AB) was used in evaluating the quality and quantity of experiments as well as the statistical significance of the variables and the model. The received data was examined and the mathematical model was used in order to find the optimal operation range for the gravure printing. The optimization of layer thickness succeeded well. The model explained and predicted the layer thickness accurately. The model validity was also tested in practice and the model was considered to be accurate. Several responses were used in order to characterize the surface roughness. However, a truly reliable model was not accomplished. The printability tests did not show any pinholes, and it is likely that there were no major pinholes on the printed surfaces. In addition, the distinctive peak values for luminance, current efficiency and external quantum efficiency were achieved.