The effect of printing ink sequence for process colors on color gamut and image quality was studied, to determine if there was an optimum printing ink sequence for flexographic printing. The results of using four process color inks (Cyan, Magenta, Yellow, and Black) in various sequences in flexography were analyzed in this research. White oriented polypropylene (OPP) film was printed with UV inks on a Mark Andy LP3000 flexo press. The sequences were analyzed based on differences in the color gamut, their volume, ability of the sequence to reproduce better-looking images, and rendering of maximum ink coverage.

The results suggest there was no one particular sequence that was proved to be optimum. Among the five sequences (YMCK, MYCK, CMYK, KYMC, and KCMY) tested, only one (KCMY) printed well without producing any moiré-like pattern. The other four sequences (CMYK, YMCK, MYCK, and KYMC) did produce a moiré-like pattern in the heavy ink coverage or shadow regions of the print. However, the sequences showing the moiré-like pattern exhibited bigger color gamuts compared to the one that does not produce a moiré-like pattern. The actual cause for the moiré-like pattern formations is unknown. It may not be due to faulty screen angles. Instead it is suspected that it is related to the wetability of the CMY inks underneath the Black. Further research is needed to find the real reason for the formations of these moiré-like patterns.

Thus, it will be difficult to have one optimum ink sequence for flexography, as one sequence may be preferable for obtaining a bigger gamut for a given hue angle, while some other sequence may produce better-looking images without any moiré-like printing artifacts appearing in the prints. If the image to be printed has more colors (requiring a bigger gamut) and limited or no shadow regions, it is recommended to print in the order of CMYK. If the image to be printed has more shadow regions, and less colors (can be printed with a smaller gamut), it is suggested to print with the KCMY sequence.