# Application of PolyJet 3D Printing in Production of Flexographic Printing Plates
## 3 Results and Discussions  
### Quality Analysis of Printing Plates  
The results of the contact angle measurements with water and diiodomethane are summarized in Table 5. Based on these measurements, the values of surface free energy and its polar and dispersive components for the printing forms were determined using the Owens-Wendt method [39]. Both materials tested showed a similar wettability with water. However, the printing plates made conventionally show a higher wettability with diiodomethane than those made with 3D printing. This resulted in a higher SFE value and indicates better wettability. Moreover, this may have a direct impact on printing, or more specifically, on ink transfer through the printing plates [40]. When making prints, this may translate into the thickness of the ink layer on the print, which can be verified by measuring the optical densities of solid areas. Nonetheless, the obtained SFE and polar component values (Table 4) for the 3D-printed and conventional plates are not different enough to translate significantly into printability [19]. Flexographic inks should wet both conventional and 3D-printed plates and properly transfer ink to the substrate. As demonstrated by the study of the shape changes of the printing point, this even slightly lower SFE value of 3D-printed plates can lead to more homogeneous ink transfer from the plate to substrate [40]. Table 6 presents the results of the chemical resistance of the printing plates. The measurements were conducted for the 3D-printed plates and conventional plates. The table presents the percentage increase in the volume of the printing plate samples after being treated with solvents for specified times (1, 2, or 4 h), based on the measured values of the width, length, and thickness of the samples. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Printing Plate** & **Made with Polylet Technology** & **Conventional** \\ \hline Water contact angle [\({}^{\circ}\)] & 74.9 \(\pm\) 1.8 & 75.4 \(\pm\) 2.3 \\ Diiodomethane contact angle [\({}^{\circ}\)] & 45.5 \(\pm\) 1.2 & 33.9 \(\pm\) 1.4 \\ SFE \(\gamma_{\mathrm{L}}\) [m]/m\({}^{2}\)] & 41.5 & 45.9 \\ Polar SFE \(\gamma_{\mathrm{L}}\)\({}^{p}\) [m]/m\({}^{2}\)] & 4.8 & 3.4 \\ Dispersive SFE \(\gamma_{\mathrm{L}}\)\({}^{4}\) [m]/m\({}^{2}\)] & 36.7 & 42.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results of measurements of contact angles of printing plates and SFE values determined from them. The designation Unk. indicates the inability to measure a parameter. This was caused by damage to the sample--tearing or crushing that made the measurement impossible. When analyzing the collected data, it is clear that the plates made using 3D printing do not exhibit adequate chemical resistance. The conventional plates showed less swelling regardless of the solvent used, although both tested materials demonstrated a low resistance to acetone and ethyl acetate. The 3D-printed plate treated with acetone was damaged after 2 h, preventing the measurement of the sample length, and the surface of the samples exhibited fractures. Conversely, after 4 h, the samples treated with ethyl acetate showed an increased brittleness, and their surfaces, similar to those immersed in acetone, were also fractured. However, it should be noted that the 3D-printed samples tested behaved correctly in undiluted water-based and UV inks--they showed a small percentage increase in volume, like the values obtained for the conventional plates. The swelling in distilled water was also negligible. Considering that 3D-printed samples exposed to more aggressive solvents exhibit a significant volume gain or even deteriorate, this disqualifies using TangoBlack Plus resin 3D-printed test plates for printing with solvent-based inks. In conclusion, the use of such a printing plate is unfortunately limited--they can be used when printing with water-based inks or UV inks. Special attention should be paid to the solvent used to wash the plate between and after printing to ensure it does not negatively affect the printing plate.