Extended color gamut printing in flexo

Extended color gamut (ECG) printing runs every job with the same fixed ink set, usually CMYK plus orange, green, and violet (CMYKOGV), and builds brand colors from those inks instead of mixing a spot ink for each one. It is also called expanded gamut or fixed-palette printing. The press stays inked between jobs, and the color work moves into prepress.

Why converters adopt it

Spot colors need custom-mixed inks and a deck washup for each job, and they stop items with different brand colors from sharing a form. Esko's Equinox reference names all three costs and notes that with a fixed set the press can use the same seven inks for every job. A Clemson study published by the FTA cites lower makeready and tooling costs as the main driver, especially where jobs can be ganged.

That makes ECG strongest for short runs, many SKUs, and packaging families that share a press. It does not suit every job.

How much of the Pantone book it covers

Coverage depends on the press, ink, and substrate. The same FTA article reports:

• About 40% of the Pantone book can be reproduced within a GRACoL CMYK gamut.
• Pantone claims about 90% with CMYK plus orange, green, and violet.
• A Clemson CMYKOGV press test reproduced 72% of the Pantone library, with an average ΔE2000 of 1.39.

Treat 90% as a vendor ceiling, not a promise for a specific press. The FTA's FIRST in Motion results note that neither ECG nor custom-mixed spot inks can match the whole Pantone book, and spot inks match more colors in most cases. ECG's advantage is predictability: from the seven-color press characterization, prepress can predict the closest achievable match for every color in the Pantone+ Solid Coated book before a plate is made.

What it takes in prepress

ECG only works on a controlled, characterized print condition:

• A specified ink set. FTA FIRST specifies pigments and hue angles for CMYKOGV sets, separately for water-based, solvent, and UV inks.
• Calibrated curves. In Esko's G7-based approach, CMYK follows the G7 dot-gain target and the extra colors print with linear dot gain. See flexo dot gain for how tone value increase is measured.
• A press characterization. The Equinox method in the FTA study prints separate target sets for CMYK, CGYK, OMYK, and CMVK, so each extra color is only sampled with its neighboring process colors.
• A fixed print sequence. The Clemson trials compared several CMYKOGV laydown orders because sequence changes the result. Keep the order the profile was built on.
• A production run that matches the profile. FIRST in Motion states the production run must match the press profile as closely as possible. A change of ink, anilox, plate, tape, or substrate can invalidate it.

Conversion software then separates each spot color into the ink channels and flags colors outside the gamut before plates are imaged. Brand colors become tints of up to three inks, so plate screening and highlight stability carry more weight than in a CMYK-plus-spot job.

When a spot color stays a spot

Keep a spot ink when a brand color falls outside the characterized gamut, when its predicted ΔE is above what the brand owner accepts, or when the job needs inks that process colors cannot build, such as metallics or opaque white. Mixed setups are common. The FTA's FIRST in Motion project printed CMYK-plus-spot and expanded-gamut versions of the same pouches in a single 10-color pressrun.

What to keep on the job record

A spot job's color lives in the ink room's formula. An ECG job's color lives in prepress decisions, so a consistent rerun depends on recording them:

• Print condition. Press, ink series, anilox, substrate, and print sequence.
• Color data. Press profile and curve versions used for the separation, plus the proof profile.
• Conversions. Each brand color, its channel build, predicted ΔE, and who approved it.
• Exceptions. Spot colors kept as spots, and the reason.
• Plates. Separation count taken from the converted file, so the plate-area quote matches what will be imaged.

When the converter re-characterizes the press, flag every open job built on the old profile. A rerun separated against a new profile can shift brand colors even when the artwork has not changed.