Rooting Out Offset Failures: Part I

In the quest for heatset web offset run efficiency, corners are sometimes cut in maintenance and quality that subvert productivity goals. Few studies have been conducted to quantify these issues, in part because press conditions vary widely, and because the market has been so much in flux.

To establish best practices for product development purposes, UPM-Kymmene, the worldwide paper producer with North American mills in Minnesota and Canada, reviewed customer complaints and examined related press conditions.

UPM also asked Omya, its ground calcium carbonate supplier, to help monitor findings. Omya's filler product is a key component for quality improvement and cost control. Calcium carbonate is far cheaper than fiber when building optical properties into a sheet.

During the last decade, more papers containing calcium carbonate have hit the market in lightweight coated reels, primarily for cost savings, but also for brightness and whiteness gains. Web offset speeds are now up to 100,000 cylinder revolutions per hour—supported by high-tech prepress and color management systems. Presses employ automatic plate changing systems, waterless printing, alcohol reduction and a variety of chemistries, running on whatever paper grade is selected.

Heatset web offset has also moved into larger formats—48-, 64- and 72-page units operate routinely today. Printing speeds of up to 66 feet per second have been achieved, from about 26 feet per second just a decade ago. Undercolor reduction is increasingly applied. Recently, heatset has grown as coldest declines, a fact that has had a big impact on quality, speed and maintenance.

Taking a wide array of printers worldwide, UPM found an even split between material-based complaints and machine- and operator-based errors. Operator error leads production complaints, with a 35% share. Paper defects (including breaks) account for roughly 30% of all print problems; ink, fountain solutions, blankets and plates represent about 15%.

Looking at paper distributions and site comparisons, sheetfed offset leads complaints with 56%; web offset has 38%. This makes sense because there is more handling associated with sheetfed, while the lion's share of web offset complaints involve web breaks. At the bottom are gravure grades, where the leading concern is also related to web breaks.

In web offset production, ink scuffing and rubbing, buckling, blistering, cracking and picking/build-up fill the middle of the complaint curve, while mottling and dusting are at the bottom.

To the paper maker, this means the importance of surface integrity is high, given the changing composition of coating materials. Although paper strength is still a big issue (and a leading source of web breaks), press conditions and operator experience in handling tension, splicing and chemistry adjustments also are contributing factors.