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Mar 28, 2012 12:00 AM
By Raymond J. Prince
Here are 9 IDEAS for curing this offset press headache
New and old presses can both be subject to streaking. Identifying the cause can be time consuming if not impossible. Generally speaking, visual examination provides no clues. Most repair personnel carry a streak chart.
Prudent printers will have a mechanic examine the press for any mechanical issues prior to implementing streaking strategies. Two basic starting points: pack the press precisely and check roller durometer. Hard rollers streak far more often than soft rollers.
Streaking isn’t covered extensively in printing standards. FOGRA in Germany uses a screen tint and cyan ink and indicates a Delta E for acceptability. Wide streaks or very narrow streaks pose complications. A penciltip sharp streak may actually have a very small Delta E while a four-inch wide streak that gradually starts and ends may have a large (but acceptable) Delta E. Not an easy problem to assign a +/- tolerance.
THE EYES HAVE IT
Finally, take a good look. Our eyes are very sensitive to any density difference or surface disturbance. Many streaks that I could see were impossible to measure with a densitometer or spectrophotometer.
Raymond J. Prince, President, GreensheetBIZ, a division of OutputLinks Communications Group, is a leading technical expert in pressroom technical and operational issues. Email him at RP@GreensheetBIZ.com.