What if there was a group of detectives able to identify and solve print problems? Bobby Congdon of Clemson University and Amy Jungerberg of Inland Packaging put together Forum 2019‘s The Defectives® with that question in mind, bringing to the stage a foursome of print experts to provide their perspectives on a half-dozen defects and their causes. They were:
- David Palmieri, director of strategic accounts & business alliances – USA, CGS gave the color and proofing perspectives
- PJ Fronczkiewicz, product manager, flexographic products, Flint Group gave the plate perspective
- Kevin Dittman, plant manager, Graphic Packaging International gave the production perspective
- Roger Poteet, president, Poteet Printing Systems gave the the ink perspective
Opening the session, Jungerberg reminded the audience that errors do happen, even when following Flexographic Image Reproduction Specifications & Tolerances (FIRST), and when they do, most important thing to do is to troubleshoot the problem and get back to printing. She then outlined the session’s scope, wherein each print problem would be examined with a six-step process:
- Describe the problem
- Collect evidence
- Consider suspects
- Rule out causes
- Identify and fix
- Prevent
When each defect was discussed, audience members were asked to share what they thought was causing the problem—the press, ink, plates or prepress. Their choices were polled live and displayed before the correct cause was revealed.
The Red Spot Defect
The first defect was a red dot appearing in a specific area of the print sample. Dittman looked at the characteristics of the defect—if it repeated, its consistency and where it first appeared—and listed out press suspects that included a damaged anilox, impression roller or even central impression (CI) drum.
Poteet posited “can ink think?” and used the question to guide his side of the investigation. If the defect is consistent, ink could be to blame, but if it isn’t, then ink is likely not the cause.
Looking at close-up images of the plates, Fronczkiewicz observed darker spots and offered possible causes: Could something be underneath the plate and causing more impression? Is a patch of dots broken?
Echoing Poteet’s examination of an area versus the entirety of the print, Palmieri argued that for the defect to be caused by prepress, it should appear consistently. “Prepress errors will not migrate position,” he said, offering color correction errors or improper image masking as possible reasons for the issue.
The cause of the defect was determined to be debris on the magenta roller and the press was to blame.
The Dirty Peppers
The second defect was several areas of the peppers that appeared dirty. Following the same order, Dittman identified a problematic color on press, and verified details like anilox volume and balanced dryers. Listing out potential causes of the defect by the press, he included incorrect anilox volume and impression setting.
Similarly, Poteet recommended an examination the ink’s pH and viscosity—the basics. “If you were using FIRST, you wouldn’t have to collect evidence—you’d already know!” he exclaimed.
Fronczkiewicz, displaying images of the plates dots, observed a discrepancy in solid ink density. He cautioned to be careful when cleaning a plate, specifically the areas where a vignette fades to zero and dots are more susceptible to breaking off from scrubbing.
After examining the original image, Palmieri explained that there were no signs of issues, no improper image masks and confirmed the correct bump had been applied.
The cause of the defect was the ink; specifically, the cyan ink’s pH had dropped to 8.4.
The Dirty Peppers: Copycat
In the third defect, two peppers in the pepper image displayed dirty print, even after the cyan ink pH was corrected. Dittman said the inks and plates were OK, colors had been identified, viscosity checked and doctor blades were replaced. He questioned if the wrong stickyback had been used or if the viscometer had malfunctioned.
Poteet, recalling his line of thinking from the first defect, pointed out that ink cannot think. Because this defect only appeared in one area of the web and was neither repeating nor consistent, it could not be ink-related.
Again comparing the dots of the target and problematic area of the print, Fronczkiewicz observed a slight disparity in solid ink density and repeated his theory that broken dots—the most common cause of plate-related defects, could be to blame.
Finding no observable issues with the original image, Palmieri listed out four possible prepress concerns that could have led to the dirty print: poor image masking, improper color conversion, an error in the color correction or an incorrect bump curve.
The press was again found to be the defect’s cause. On one side of the press, air was found blowing across the gear side of the black plate.
Needs More POP!
Defect No. 4 spotlighted a favorite of brand owners—a lack of “pop” in the peppers image. On the press side, Dittman observed a noticeable difference between the magenta’s target density and the density measured in the defect. He suspected the anilox used was either incorrect or plugged/dirty.
In discussing the ink’s role, Poteet noted the defect is less saturated, especially in its red areas, and backed Dittman’s concern over the magenta density. He reiterated his question “Can ink think?” and, in this case, pointed to the defect’s presence across the entire image. He wondered aloud the anilox’s volume and the ink’s transfer characteristics.
Observing no visible issue with the printed dots, Fronczkiewicz considered an incorrect surface screening, imaging defect or too-soft tape as being responsible for the defect.
On the prepress side, Palmieri focused in on the magenta and yellow (“What creates red?” he asked the audience), and suggested the wrong curves could have been applied, or there could be an issue with the RGB-to-CMYK conversion.
Dittman’s initial suspicion came to pass, as the wrong anilox was loaded into the press (a 1.8 instead of a 2.2). “I promise you, the press knows the difference between a 1.8 and a 2.2,” Poteet said.
No, The Real Death Valley
The next defect the group referred to as “No, The Real Death Valley,” where an image of a tiger was visibly off in its color, both in the final print and in each color separation. Dittman speculated the wrong volume anilox could have once again been used, or coating saturation could be to blame.
Poteet listed out again his basic steps to examining the ink’s potential role, including its pH, viscosity and formulation.
Fronczkiewicz, finding no fault with the plate and very close solid ink density measurements, posited that a round top plate was used instead of a flat top, which could have led to smaller dots.
Comparing 1-bit TIFFs and the actual print, and the target and defect samples, Palmieri found across-the-board differences at 50 percent. He identified the wrong curves, a bad RGB-to-CMYK conversion and overall poor color correction as possible causes of the defect.
And his first hunch bore out, as the prepress department used the incorrect LEN files and the wrong curves were applied to all colors.
Mutated Mascot
“It’s not right to do this to a tiger,” joked Clemson graduate Dittman as he began investigating the sixth and final defect, in which the printed image of a tiger contained some off-target colors, but not all. He verified kiss impressions and the pressroom’s conditions, and wondered if the operator had not followed the setup sheet or some non-standard SOPs were followed.
Poteet ran through his checklist and discovered that the magenta’s density was less than the target, while cyan, yellow and black were all greater.
Fronczkiewicz observed cupping in the midtones (a camelback curve) and pointed out that certain flat top processes and plates can be very reactive and prone to dot cupping.
Examining the source image and dot structure, Palmieri found nothing which pointed to prepress’ culpability.
At last, plates were found guilty of causing a defect. Here, the magenta plate was overexposed, causing dot cupping.
“Always make sure to look beyond the first thing you see,” Jungerberg said in closing the session. “Go beyond that, continue to ask questions, continue to investigate and narrow down. Jumping to conclusions can get you into trouble.”