The intelligent use of ink sets promotes better accuracy on press and minimizes the visual effect of press drift during long pressruns.
That is what’s indicated in the results from a new study at Ryerson University, Toronto, using its 7-color, narrow web, Comco Cadet label press with Esko Equinox and GMG OpenColor solutions, to test reproduction of 30 different Pantone+ Solid Coated spot colors on extra gloss LTR label stock.
As we all know, expanded gamut printing (EG) refers to the use of CMYK + orange, green and violet (OGV) colorants, and is applicable to all printing processes—flexographic package printing, offset folding cartons, an HP Indigo digital label press or an Epson inkjet proofer. For a customer’s job requiring spot colors, EG offers major cost savings. Why?
- Many spot colors can be realized with an EG ink set
- There is no need to estimate, formulate, ship, store, make plate separations, ink and de-ink the press with a spot color ink
- Printers can simply leave CMYKOGV inks in the ink train and print different spot colors all day long
EG printing offers increased stability and accuracy on press, especially for long pressruns. In CMYKOGV printing, we can choose colorants that are very close to the customer’s requested color. So, in the case of a client like McDonald’s, we make the yellow of the “golden arches” with green, yellow and orange, and drift in any of these inks over a long pressrun does not annoy our favorite fast food vendor. Consider how offensive a similar amount of drift in cyan (a blue color) would be, if using traditional CMYK printing!
Oh, and of course, the use of additional colorants—OGV—does expand the color gamut, compared to a conventional CMYK ink set. That means we can simulate many spot colors in an EG process, but the gamut expansion is not the primary advantage of EG printing.
We contend that EG primarily offers cost savings, increased stability and accuracy on press, and incidentally expands the color gamut in the process. April Burke, VP operations, Bellwyck Packaging, Toronto says, “We see EG as allowing us to drive down costs, improve quality and reduce turnaround time for our premium and pharma packaging clients.”
Previously, Ryerson University had evaluated and tested EG printing systems for the HP Indigo 7900 and Epson SureColor P9000 using 10 different color management solutions (see “Ryerson’s Research,” FLEXO Magazine, November 2019. A free, 50-page comprehensive report is still available).
The flexographic community uses a myriad of terms when describing the steps for color management. One recent article covered all eventualities with terms including standards, characterization, target, fingerprint, optimization, baseline, linearization, ICC profile, GRACoL, FOGRA, Flexographic Image Reproduction Specifications & Tolerances (FIRST), etc.
We define color management in flexography as consisting of four steps, and let us call each step by what it actually is. We consider the process of color managing a flexographic printing process (4-color or 7-color) as follows.
- Press optimization
- Curve calibration
- Color characterization
- Verification/customer job
In our color management project, flexographic plates were made using the CDI system, and press optimization was carried out to establish optimum plate and anilox characteristics, ink viscosities, print densities and screen angles. The goals:
- Match the nature of the graphics in the file to the plate lpi to the anilox bcm
- Avoid moiré
- Maintain highlight dot strength and resolution
- Establish optimum printing conditions without “leaving money on the table”
Next, a curve calibration pressrun is done where the inherent characteristics of the plate printing system are determined and software is used to change the raw state to a new preferred state. Curve calibration is built into all software and most commonly is used to change the default behavior to G7 for the CMYK channels, while leaving the OGV separations linear in terms of SCTV. Note that the curve calibration step is a one-dimensional correction (1-D LUT), which means that it works on each channel separately. This means curve calibration deals primarily with tone curves and tonal response.
The true color management part of the process starts with color characterization, which uses a characterization chart that is printed and measured to determine the color characteristics of the printing process. Different software systems have their own color characterization charts, and after printing and measuring the chart, the software uses this data to create proprietary multidimensional LUTs or a non-proprietary ICC profile.