# Application of PolyJet 3D Printing in Production of Flexographic Printing Plates
## 3 Results and Discussions
### Quality Analysis of Printing Plates

Table 7: ANOVA test results for optical density values for different types of printing plates. Figure 6: Optical density values of prints made with different printing plates (F1–F5), various raster cylinder rulings (L160 and L200), and multiple printing substrates (P1–P6). the conventional printing plates F4 and F5. Furthermore, the solid areas printed with the 3D-printed flexographic plates had a lower optical density compared to the prints from the conventional plates. The differences in optical densities were greater for the measurements of the prints obtained using a 200 lpc raster cylinder ruling. For the coated substrates, they range from 0.10 to 0.30, while for the uncoated substrates, the difference is greater, ranging from 0.2 to 0.4 depending on the substrate. The \(L^{*}\), \(a^{*}\), \(b^{*}\) color coordinate measurements indicate that the reproduced colors vary significantly among the different prints (\(0.1\leq\Delta\mathrm{E}\leq 58.4\)). Notable variations in lightness (\(L^{*}\)) values were confirmed by the ANOVA test results (F (59, 540) = 1.346, \(p=0\)). The prints made with the 3D-printed flexographic plates are lighter and less saturated compared to those obtained with the conventional plates (Figure 7). Moreover, similar to the D value, both the printing substrate and the raster cylinder ruling used significantly affect the results. Consistent with the optical density findings, the results of the measurements for the prints obtained using a raster cylinder ruling of 200 lpc are lighter than those obtained with a ruling of 160 lpc, which is directly related to the inkwell capacity of the cylinders--cylinders with smaller linings have larger inkwells, allowing for greater ink transfer. Considering the printing substrates, the uncoated substrates (P3 and P5) yielded significantly higher \(L^{*}\) values, i.e., lighter prints, compared to those made on coated substrates. This difference can be attributed to the variations in substrate absorbency. Additionally, the use of 3D-printed flexographic plates led to even higher \(L^{*}\) values (differences of up to 15-17%). These variations in lightness significantly impact the resulting color. In analyzing the measurements of percentage coverage, it is evident that full consistency cannot be achieved on any of the considered substrates, regardless of the raster cylinder used (Figure 8). The highest level of agreement in the measurements was observed for the coated substrates at fields with 75% coverage. The 3D-printed flexographic plates of 34 lpc (F1) correlated with the conventional plates labeled 4-5, which correspond to 42 lpc and 38 lpc, respectively. The measurements of the degree of percentage coverage for a 3D-printed flexographic plate of 20 lpc (F2) for fields of 75% are lower than the averages for the conventional plates. The percent coverage rate for the uncoated substrates has a value lower than the conventional plates for both 3D-printed flexographic plates and raster cylinders. Regarding the percentage coverages of 50% and 10%, we cannot speak of the correct reproduction. Some correlation of the measurement results was noticeable, but this is insufficient due to the lack of visual mapping. Unfortunately, the 3D-printing technology and the resin used did not allow us to obtain the correct raster points on the flexographic plates and reproduce them in the printing process. Figure 7: Average lightness of prints obtained on multiple substrates (P1–P6) using different printing plates (F1–F5) and various raster cylinder rulings of (**a**) 160 lpc and (**b**) 200 lpc.