Ruoxi "Rachel" Ma

Color Gamut Extension on 4-color Sheet-fed Offset Press Using Ink Fountain Divider Methodology

Ruoxi Ma and Brian Lawler, California Polytechnic State University

The advancement in technology and the necessity to satisfy the increasing quality requirements has called for the use of extended color gamut in offset printing. The color gamut of 4-color offset press was vastly extended by using the ink fountain divider to separate the ink fountain tray on each color unit. Other than the offset C, M, Y, K ink cartridges, the project includes the pantone orange, violet and green offset ink to develop an innovative method of extending the color gamut of 4-color offset press by transforming it into a 7-color half width offset press.

In this study, a test chart was created with ProfileMaker. The test chart was printed on Heidelberg SpeedMaster CD 74 on glossy coated paper. The press was setup with 2 color inks on the second, third and fourth unit by using an ink divider in the middle of each ink fountain tray. The C, M, Y, K, Pantone Orange, Violet and Green will be printed with 2 passes on the same side of substrate, flipped from left to right, bottom to up.

This method of printing will lead to huge enhancement in the measured color gamut, which in this case provided by the KCVMOGY (Black-Cyan-Violet-Magenta-Orange-Green-Yellow) inks. However, this print method will also reduce the width capacity of the substrate on this press to half of its current capacity. For example, the biggest substrate width of Heidelberg CD 74 is 74cm, with the 7-color setting, the biggest substrate width will be 37cm instead.

The printed results will be characterized by measuring the CIELAB values and the reflectance spectra with an X-Rite i1iO spectrophotometer with 45°/0° geometry. Profile Maker will be  used to make the ICC profiles for the ink and substrate combinations. Color volumes will be created by ColorThink Pro. The KCMY color gamut and KCVMOGY color gamut will be compared accordingly.

The purpose of this study is to investigate a new way to utilize a wide format 4-color offset press to print a wider color gamut. Printing with 7 color creates a wider color gamut with more vivid area and more depth in color. This methodology could be used on the Heidelberg SM CD74 or any other wide format 4 color offset press to output 4+ color job with less trimming waste and wider color gamut.