# The Impact of Underlying Opaque White Coating Parameters on Flexographic Print Quality
## 5 Conclusions  
When printing transparent substrates, a white ink underlayer is required to reproduce saturated colors. The white ink has a pronounced effect on color perception that is printed over it. The change in opacity of color samples is related to their brightness. According to the conducted research, the increase in white ink opacity from 42% to 44% in the second stage of the experiment was very slightly visually noticeable in color samples on printouts (\(\Delta\)E2000 = 0.5-1.0). This means that 1.3 times the amount of white ink was needed without any improvement in the final results. However, a visually noticeable change in color samples (\(\Delta\)E2000 = 2.0-2.7) occurred due to the increase in white ink opacity from 42% to 49% in the third stage of the experiment (1.6 times larger amount of white ink was needed). This can significantly increase the production costs of the final product. On average, an increase in opacity of 1% requires an increase in anilox roller volume of 1.2 cm\({}^{3}\)/m\({}^{2}\).  
Medium lightness colors (cyan, magenta, and red P 485 C) more strongly reacted to changes in white ink opacity compared to light (yellow) and dark (black) colors. It can be concluded that light colors require a higher opacity of the white ink layer in order to comply with the defined standards and look the most faithfully possible on the print. Therefore, it is not possible to speak generally about the acceptable value of white ink opacity in print, since it significantly depends on the color scheme that was applied in the product design.  
Also, the distribution of the white ink on the printing substrate significantly impacted the quality of the print. A thicker white ink layer had a more uniform distribution of the ink, which also meant a smoother surface and a less pronounced pinholing effect. Therefore, such a surface reflected more light and looked lighter. Also, colors printed over white had significantly better characteristics. All color samples were lighter compared to the referent state (\(\Delta\)L = 1.7-2.8); only the black color was darker (\(\Delta\)L = \(-\)2.2). Furthermore, by increasing the volume of the anilox roller for white ink, the lightness increased more in the lightest color samples. For example, there was a greater increase in yellow (\(\Delta\)E = 2.7)  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Number of Pinholes**} \\ \hline
**Pinhole Area** & \multicolumn{3}{c}{**Anilox Roller Volume (cm\({}^{3}\)/m\({}^{2}\))**} \\ \cline{2-4}
**(\(\upmu\)m\({}^{2}\))** & **10** & **13** & **16** \\ \hline
100–199 & 34 & 9 & 1 \\
200–299 & 18 & 1 & 0 \\
300–399 & 11 & 1 & 0 \\
400–499 & 3 & 0 & 0 \\
500–999 & 6 & 1 & 0 \\
1000 and more & 7 & 0 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Number of pinholes at three stages of the experiment.  
compared to magenta (\(\Delta\)E = 2.0). However, a thicker white ink layer can create additional issues in printing, as well as issues with the smell of packaging material.  
The white ink can have extremely high opacity, but if the ink layer is not uniform, and has a significant number of pinholes on the print, this can contribute to creating a bad visual effect. Therefore, in order to achieve high print quality, the pinholing effect must be taken into account, in addition to high white ink opacity. The evaluation of qualitative reproduction parameters gave important indicators that can significantly improve the production process and result in increased quality.  
Project administration, supervision and conceptualization, R.T. and D.V. ([PERSON]); investigation and methodology, D.V. ([PERSON]) and M.T.; resources, R.T.; visualization and validation, D.V. ([PERSON]); writing--review and editing, R.T., D.V. ([PERSON]), M.T. and D.V. ([PERSON]). All authors have read and agreed to the published version of the manuscript. This research received no external funding.  
Not applicable.  
Measurement data are available per request by corresponding author email.  
The authors declare no conflict of interest.