Press Cycles

 

presses fluctuate in dot gain

By now, if you have been paying attention, you have probably come to realize that an offset printing press cannot be controlled through density alone.  The success of the G7 process has demonstrated that gray balance is the single greatest determiner of color appearance; and while a number of different factors contribute to gray balance, it is primarily determined by dot gain, or TVI.

TVI is now recognized by most quality printers as the most important control point to correct gray balance appearance and thus overall color accuracy.  But many printers have also learned that dot gain, or TVI, doesn’t stand still. It is subject to frustrating variation overtime that can have negative effects on color accuracy and makeready times. Curves that were meticulously created for perfect gray balance during G7 Master Printer Qualification often prove near-useless only a month or two later, causing some printers to even question the validity of the entire G7 concept.

One if the difficulties of G7 Master Printer Qualification is caused by a sort of “Observer Effect”. Since all concerned are on their best behavior during a fingerprint, or characterization press run, results are liable to change once the printer returns to actual work conditions. Bottom line: a single press run is a very poor predictor of long term TVI or dot gain, behavior, and consequent gray balance results, especially if that press run was done with an “Expert” on site.

In order to control press performance, we must know not just how the press was performing on the special day of G7 qualification, but how it is performing at any given moment. Equally important, we must know the status of mean performance over time. So how can we get around the  Observer Effect and view real press performance in a meaningful way?

Here are 5 quick tips for achieving the best possible results from your offset press in real production:

  1. Never rely on a single press run to determine plate curves.
  2. The more careful and painstaking the fingerprint or characterization run, the less likely it is to represent real press performance.
  3. Track TVI or dot gain on every press run, not just “special occasion” jobs.
  4. Use process control software to collect and average dot gain results over time.
  5. Remember a press rarely prints perfectly. Your best effort is to see that results are slightly high about 25% of the time, slightly low about 25% of the time and near-perfect the rest of the time.

 

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