# Application of PolyJet 3D Printing in Production of Flexographic Printing Plates
## 2 Materials and Methods
### Printing Plates  
The printing plates for the study were created using both Polylet additive manufacturing technology and the traditional photopolymer technology typically used in the industry for producing flexographic plates. Figure 3 illustrates a comparison of the two methods of making printing plates.  
The Polylet test plates were produced on an Objet Connex350 machine (Stratasys, Tucson, AZ, USA) using TangoBlackPlus FLX9870-DM (Stratasys, Tucson, AZ, USA) photoresin. The resin has the following properties: hardness 68-72 Sh A, tensile strength 3.5-5.0 MPa, elongation at break 65-80%, and tensile tear resistance 15.5-17.5 Kg/cm. The plates (Figure 4a) were printed by RapidPro Company (Wroclaw, Poland) based on the provided files containing digital models of the plates (Figure 2). Printing was done in high-quality modes and the layer height was 0.016 mm. The support material was removed using pressurized water at the post-processing stage.  
The test printing plate was 90 mm wide and symmetrically divided into two zones of different linearity--it consists of two identical tests with a 6 mm notch between them. This notch is due to the design of the raster cylinder of the RK Print Flexiproof (RK Print Coat Instruments Ltd., Royston, UK) used for printing. The thickness of the printing plate was 1.7 mm, and the depth of the relief was 0.5 mm. Additionally, 10 samples of size 20 mm \(\times\) 10 mm \(\times\) 1.7 mm were printed for surface tension and chemical resistance tests of the test printing plate.  
A 1.7-mm-thick photopolymer conventional plate nyloflex(r) FAH (BASF SE, Warsaw, Poland) (Figure 4b), prepared by Chespa (Chorula, Poland), was used for the comparative study. The conventional plate consisted of 6 tests with different screen rulings.  
Further characteristics of the printing plates are presented in Table 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **g [mm]** & **L [mm]** & **SN [\%]** \\ \hline Value & 1.7 & 260 & 4.11 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Calculation of percentage shortening in printing direction.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Percentage** & **Point Area [mm\({}^{2}\)]** & **Single Point Radius [mm]** &
\begin{tabular}{c} **Raster Point Radius in** \\ **Printing Direction [mm]** \\ \end{tabular} \\ \hline \hline \multicolumn{4}{c}{Test plate with 20 lpc linearity} \\ \hline
10 & 0.0250 & 0.0892 & 0.0855 \\
50 & 0.1250 & 0.1995 & 0.1913 \\
75 & 0.1875 & 0.2443 & 0.2343 \\ \hline \hline \multicolumn{4}{c}{Test plate with 34 lpc linearity} \\ \hline
10 & 0.0087 & 0.0525 & 0.0503 \\
50 & 0.0433 & 0.1173 & 0.1125 \\
75 & 0.0649 & 0.1437 & 0.1378 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Raster point size calculations for 3D-printed flexographic plates.  
Figure 4: Photos of printing plates: (**a**) 3D-printed with linearity of 34 lpi and sample for chemical resistance testing and (**b**) conventional photopolymer with linearity of 42 lpi.  
Figure 3: Schemes for making flexographic printing plates (**a**) traditional photopolymer, and (**b**) 3D-printed using Polylet technology.