Wet trap and colour sequence on sheetfed offset

Trap is a film sandwich

Wet trap is how much of the next ink sticks to the still-wet film underneath. Typical sheetfed sequences put yellows and lighter films down early and the strongest, tackiest dark last—unless the house standard says otherwise.

If you print a brand red last on a heavy cyan, the red can look dirty even when each solid density is “to spec.” Measure trap if you have a spectro; if not, look at the overprint patch on the control bar.

• Agree sequence on the ticket before make-ready.
• A Honglu spot may need its own unit and a trap test on the live inks.
• LOCOER intermediate bases exist to mix spots; they still trap as films.
• Too-fast set on a closed board can kill trap of the next colour.
• G7 grey balance assumes a sequence you can repeat.

Process versus spot

Process CMYK trap is a daily habit. A metallic or fluorescent last-down is a special case—see the effect-ink article. Do not trap a metallic into a wet black without a trial.

Tack staircase

Some plants run decreasing tack through the units so each next ink can split. Seasonal temperature breaks that staircase. Log hall temperature with the sequence.

What to send HuiRun

Sequence, whether the job is process-plus-spot, and a scan of the failed overprint. We can suggest a different conventional tack grade or a Honglu spot placement. We cannot trap the job from Hefei.

What the quote covers

Trap percentages in a maker brochure are laboratory prints. Your blankets and speed own the number.