# The Impact of Underlying Opaque White Coating Parameters on Flexographic Print Quality
## 4 Results and Discussion  
### Analysis of White Ink and Color Ink Opacity  
The results of measuring white ink opacity and selected color samples' opacity are shown in Table 3, and were obtained as the average value of five measurements. The printing experiment took place in three stages that had constant printing conditions, thus enabling the investigation of a variable parameter, which was the volume of the anilox rollers. The first stage used an anilox roller with a volume of 10 cm\({}^{3}\)/m\({}^{2}\), and it was increased by 3 cm\({}^{3}\)/m\({}^{2}\) through the remaining two stages of the experiment. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(k\) & \(\Delta E_{min}\)**(_k_)** & \(\Delta E_{max}\)**(_k_)** & **Perception of Color Differences** \\ \hline
1 & 0.0 & 0.5 & Hardly \\
2 & 0.5 & 1.5 & Slight \\
3 & 1.5 & 3.0 & Noticeable \\
4 & 3.0 & 6.0 & Appreciable \\
5 & 6.0 & 12.0 & Much \\
6 & 12.0 & 24.0 & Very much \\
7 & 24.0 & \(\infty\) & Strongly \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Subjective assessment metric based on CIEDE2000 Color difference [35]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{4}{c}{**Opacity (\%)**} \\ \hline \hline \multirow{2}{*}{**Color Samples**} & \multicolumn{3}{c}{**Anilox Roller Volume (cm\({}^{3}\)/m\({}^{2}\))**} \\ \cline{2-4}  & **10** & **13** & **16** \\ \hline C & 51.53 & 53.46 & 57.8 \\ M & 48.52 & 50.35 & 54.68 \\ Y & 44.45 & 45.4 & 49.99 \\ K & 60.23 & 61.1 & 67.35 \\ R & 50.55 & 52.4 & 56.77 \\ W & 42.08 & 44.33 & 49.47 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Ink opacity throughout three stages of the experiment with different anilox volume. The increase in the white ink opacity (Table 3) was directly related to the anilox roller volume for white color, while the increase in the opacity of the color samples related to the white ink opacity. The diagram from Figure 5 primarily shows the change in the white ink opacity (W) due to the increase in the ink layer, which resulted from the increase in the anilox roller volume. Anilox roller volume of process colors (CMYK) and spot red P 485 C color (marked as R in tables and figures) was constant throughout all three printing stages, which means that their relative opacity also did not change. However, as the opacity of the opaque white ink increased, the absolute opacity of the process colors and the spot red P 485 C color increased. Generally speaking, yellow as the lightest color had the lowest opacity, and black as the darkest color had the highest opacity. This effect can be attributed to the physical fact that yellow has the lowest blocking power of all inks. As a result, yellow is more dependent on a white undercoat to block background colors (in this case, a black backing) than other colors. A linear increase in the volume of the anilox roller by 3 cm\({}^{3}\)/m\({}^{2}\) (2 BCM) during the experiment did not result in a linear increase in the white ink opacity. The curve was slightly exponential. Increasing the volume from 10 cm\({}^{3}\)/m\({}^{2}\) (O = 42.08%) to 13 cm\({}^{3}\)/m\({}^{2}\) resulted in an increase by 2% (O = 44.33%) in opacity, while a further increase to 16 cm\({}^{3}\)/m\({}^{2}\) caused an increase in opacity by 5% (O = 49.47%). The curves of the tested color samples show a similar trend in increasing opacity. However, this increase was less exponential compared to white ink. Figure 6 shows the absolute increase in opacity based on the linear increase in the volume of the anilox roller in the last two stages of the experiment in relation to the reference values from the previous stages of the experiment. The diagram in Figure 6 shows that the total white ink opacity in the third stage of the experiment significantly increased the opacity of the colored samples (around 4.5%) compared to the second stage of the experiment (about 1-2%).