# Application of PolyJet 3D Printing in Production of Flexographic Printing Plates
## 3 Results and Discussions
### Quality Analysis of Printing Plates
Evaluation of the Quality of Prints Made with Conventional Plates and Printed with Polylet Technology  
The evaluation of the quality of the prints included an analysis of the optical density (D) values of the solid fields, the \(L^{*}\), \(a^{*}\), \(b^{*}\) color coordinates, and the changes in the coverage of the raster fields (tone value changes). The effect of the type of flexographic printing plate, as well as the printing substrate and anilox ruling on the optical density values are shown in Figure 6.  
The ANOVA test results for the optical density values (F(59, 540) = 1.346, \(p\) = 0) indicate significant differences between the group averages. The magnitude of the differences between the obtained values is significantly influenced by the raster cylinder ruling (F(29, 270) = 1.510, \(p\) = 4.1 \(\times\) 10\({}^{-196}\) and F(29, 270) = 1.510, \(p\) = 3.3 \(\times\) 10\({}^{-186}\) for L200 and L160, respectively). The prints with a 160 lpc cylinder ruling showed higher D values due to the higher ink capacity of their inkwells, resulting in more ink being transferred to the printing substrates. Moreover, the conducted analysis revealed a significant influence of the type of flexographic printing plate on the obtained optical density results (Table 7). No significant differences were observed between the prints made using 3D-printed plates F1 and F2 regardless of the substrate and ruling type. Similarly, the prints made using the conventional \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Solvent**} & \multicolumn{4}{c}{**3D-Printed Plate**} & \multicolumn{4}{c}{**Conventional Photopolymer Plate**} \\  & **After 1 h** & **After 2 h** & **After 4 h** & **After 1 h** & **After 2 h** & **After 4 h** \\ \hline Water & 2.79 & 0.55 & 1.96 & 1.52 & 0.45 & 1.21 \\ Acetate & 73.03 & 111.87 & 141.05 & 34.57 & 50.25 & 63.15 \\ Ethanol & 21.98 & 30.54 & 42.35 & 1.84 & 0.90 & 1.97 \\ Acetone & 89.10 & Unk. & Unk. & 12.43 & 15.80 & 21.11 \\ Isopropanol & 14.70 & 21.32 & 30.20 & 3.61 & 3.74 & 4.08 \\ Npropanol & 15.26 & 27.59 & 38.45 & 5.85 & 5.93 & 6.44 \\ Chesol & 22.02 & 31.48 & 48.69 & 1.21 & 9.49 & 8.71 \\ Water-based ink & 0.99 & 1.14 & 0.29 & 0.48 & 1.46 & 0.89 \\ Solvent-based & 23.07 & 38.93 & 56.69 & 7.28 & 6.86 & 6.09 \\ ink & 0.17 & 1.49 & 1.94 & 0.53 & 1.78 & 2.38 \\ \hline \end{tabular}  
* Unk.—means the inability to measure the sample due to damage.  
\end{table} 
Table 6: Percentage increase in volume of samples. plates (F3, F4, and F5) showed no significant differences in their optical densities, except for a few cases: F3/F4 on the P1 substrate, and F3/F4 and F3/F5 on the P3 substrate, for prints made with L160 cylinder. On the other hand, the prints made with the 3D-printed flexographic plates exhibited significant differences in D values compared to those made with the conventional plates. Only the prints obtained using a 3D-printed plate with a 34 lpc (F1) ruler and a 160 lpc raster cylinder did not differ significantly from those obtained using the same raster cylinder and \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Printing Substrate**} & \multicolumn{2}{c}{**Raster Cylinder**} \\ \cline{2-3}  & **200 lpc** & **160 lpc** \\ \hline P1 & F(4, 45) = 2.579, \(p\) = 7.67 \(\times\) 10\({}^{-21}\) & F(4, 45) = 2.579, \(p\) = 3.28 \(\times\) 10\({}^{-5}\) \\ \hline P2 & F(4, 45) = 2.579, \(p\) = 6.76 \(\times\) 10\({}^{-11}\) & F(4, 45) = 2.579, \(p\) = 1.94 \(\times\) 10\({}^{-6}\) \\ \hline P3 & F(4, 45) = 2.579, \(p\) = 2.17 \(\times\) 10\({}^{-12}\) & F(4, 45) = 2.579, \(p\) = 1.60 \(\times\) 10\({}^{-6}\) \\ \hline P4 & F(4, 45) = 2.579, \(p\) = 1.03 \(\times\) 10\({}^{-24}\) & F(4, 45) = 2.579, \(p\) = 8.02 \(\times\) 10\({}^{-25}\) \\ \hline P5 & F(4, 45) = 2.579, \(p\) = 8.58 \(\times\) 10\({}^{-9}\) & F(4, 45) = 2.579, \(p\) = 1.37 \(\times\) 10\({}^{-7}\) \\ \hline P6 & F(4, 45) = 2.579, \(p\) = 1.01 \(\times\) 10\({}^{-16}\) & F(4, 45) = 2.579, \(p\) = 4.20 \(\times\) 10\({}^{-15}\) \\ \hline \hline \end{tabular}
\end{table}