Abstract

Gamut is defined as a subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a certain output device.

Printing technology has advanced quite rapidly—particularly in packaging. Improved inks, plates, anilox rolls, presses, prepress applications and separations have enabled converters to move from the traditional limitation of ‘spot’ colors, to a more expanded, advanced, computerized screen and process printing technique using process inks.

This has led printers to consider implementing expanded gamut. Expanded gamut is the use of producing a wider set of colors by adding more than the traditional set of CMYK process inks. The process of expanded gamut is very attractive to printers who, if not constrained by replacing brand color inks after every press run, can speed up makereadies because they do not have to clean ink units on press. More significantly, they can gang jobs together, because ink colors are not created by special inks, but just process builds.

Until recently, particularly with flexo printing, the biggest concern with this practice was the stability of the plates and presses. Could they consistently and predictably hold the dots to assure accurate reproduction within tight tolerances of important colors—like those required by brands and traditional solid Pantone inks? However, improved inks, plates, anilox rolls, presses, prepress applications and separations have enabled converters to move from the traditional limitation of ‘spot’ colors, to a more expanded, advanced, computerized screen and process printing technique using process inks.

Introducing three more inks into the process, traditionally orange, green and violet, can split the hue components from three to six sections. Rather than relying on yellow and cyan to derive a shade of green, now a printer can rely on mixing yellow and green together—or cyan and green. Since they are closer to each other in hue, they can represent more colors, more accurately.

We also know that by implementing GCR (Gray component replacement), shifts in colors on press may not affect results as severely as pure color builds. Our objective was to determine, through press trials, the effect of press variation on color stability with 4-color and 7-color process color tint builds. At the same time, we decided to see how the implementation of GCR affects stability on press.

Inks act as levers on the color tint build. However, the more the inks, the shorter the levers are on that build: This is easy to explain. The differences in hue are further apart with a four-color ink set than a seven-color ink set. In the diagram below, you can see that the difference in hue between cyan and yellow is 140.3°, but only 86.4° between green and yellow. There are also differences in chroma

So, our research project attempted to prove three hypotheses. First the maximum GCR results in the least color variation. Second, we believed that color build logic using 7C and Maximum GCR would result in the least color variation. We also felt that a 7C build logic would result in the lowest ink consumption. We selected 300 different ink builds—both 7C and 4C, represented evenly throughout the entire color gamuts.