## 3 Results and Discussion
### Cupping Test  
The results shown in Table 7 and in Figure 9, in the case of samples equipped with barrier protection, express the formation of cracks in the given coating; in the case of the other samples, it is the formation of surface cracks in the base material. As the water-based coating delaminated before the end of the degradation test, the indentation value could not be determined. Figure 8: Nature of the sample failure after the degradation test (impact test): (**a**) Chemical smoothing (84.97 kJ\(\cdot\)m\({}^{-2}\)); (**b**) heat treatment (88.53 kJ\(\cdot\)m\({}^{-2}\)); (**c**) epoxy resin (82.71 kJ\(\cdot\)m\({}^{-2}\)); (**d**) synthetic coating (85.29 kJ\(\cdot\)m\({}^{-2}\)); (**e**) water-based coating (81.49 kJ\(\cdot\)m\({}^{-2}\)); (**f**) standard-recycled rPET-G (77.60 kJ\(\cdot\)m\({}^{-2}\)). The achieved results again confirm the positive effect of annealing on the increase in adhesive forces between the printing layers. Furthermore, a slight negative effect of the chemical smoothing on the elasticity of the material was statistically confirmed, which, on the other hand, was not proven by the measurement of the impact strength. However, this finding can be justified again by the dimensions of the test samples, since the thickness of the material for the indentation test is only 1.6 mm. The ratio of the content of the cross-section treated with the etchant to the content of the cross-section of the tough core is therefore significantly higher than in the case of the sample intended for the determination of the impact strength. Furthermore, the unsuitability of epoxy resin for components subjected to external forces was again confirmed, as the coating already breaks when deepening in the range of approx. 3-4 mm. In this respect, even the synthetic coating is not very suitable, but the achieved results correspond with the deepening values of synthetic coatings applied to a standard steel substrate [40]. On the contrary, in the case of a water-based coating (before the degradation test), the failure of the coating can be justified by the adhesion failure between the printing layers in the substrate. The appearance of surface cracks in the coating occurs at a statistically almost identical depth as in the case of the standards. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{8}{c}{**Quantity**} \\ \hline  & \multicolumn{8}{c}{**Testing Phase**} \\ \hline  & \multicolumn{2}{c}{**AM, mm**} & \multicolumn{2}{c}{**D, mm\({}^{2}\)**} & \multicolumn{2}{c}{**SD, mm**} & \multicolumn{2}{c}{**CV, \%**} \\ \cline{2-9}
**Type of PP** & \multicolumn{2}{c}{**Before**} & \multicolumn{2}{c}{**After**} & \multicolumn{2}{c}{**Before**} & \multicolumn{2}{c}{**After**} & \multicolumn{2}{c}{**Before**} & \multicolumn{2}{c}{**After**} \\ \cline{2-9}
**CS** & 6.88 & 5.20 & 0.2079 & 0.4277 & 0.456 & 0.654 & 6.63 & 12.58 \\
**HT** & 9.50 & 7.95 & 0.1866 & 0.3080 & 0.432 & 0.555 & 4.55 & 6.98 \\
**ER** & 3.95 & 3.05 & 0.1429 & 0.3422 & 0.378 & 0.585 & 9.57 & 19.18 \\
**SC** & 5.12 & 4.25 & 0.1592 & 0.3215 & 0.399 & 0.567 & 7.79 & 13.34 \\
**WBC** & 8.20 & - & 0.2540 & - & 0.504 & - & 6.15 & - \\
**WPP (rPET-G)** & 8.50 & 5.90 & 0.1665 & 0.4122 & 0.408 & 0.642 & 4.80 & 10.88 \\
**WPP (PET-G)** & 8.67 & 6.05 & 0.1945 & 0.3672 & 0.441 & 0.606 & 5.09 & 10.02 \\ \hline \hline \end{tabular}  
* PP—Post-processing; CS—Chemical smoothing; HT—Heat treatment; ER—Epoxy resin; SC—Synthetics coating; WBC—Water-based coating; WPP—Without post-processing: AM—Arithmetic mean; D—Dispersion; SD—Standard deviation; CV—Coefficient of variance.  
\end{table} 
Table 7: Evaluation of the cupping test (before and after 60 degradation cycles). Figure 9: Rate of deepening before and after the degradation (arithmetic mean \(\pm\) standard deviation). This phenomenon is nothing exceptional, as it has also been recorded, for example, in the case of applying a water-based coating to a hot-dip galvanized steel sheet [38]. The water-based coating, therefore, exhibits very high elasticity.