Forum 2018’s final session, “Troubleshooting Survival Guide,” provided a comprehensive look at common and persistent problems faced by flexographers, with solutions for both immediate and long-term fixes.
Chaired by Catherine Haynes of All Printing Resources Inc (APR) and 2018 FTA President’s Award recipient Jason Cagle of MacDermid Graphics Solutions, the session featured an expert panel that went over everything from matching color to proofs, to high dot gain, and more.
That panel included:
- Bobby Congdon, Clemson University, speaking from the color perspective
- Joel Engelberth, Esko, speaking from the prepress perspective
- PJ Fronczkiewicz, Flint Group, speaking from the plate perspective
- Kevin Dittman, Graphic Packaging International, speaking from the pressroom perspective
Catherine opened the session with brief overview of the importance of Flexographic Image Reproduction Specifications & Tolerances (FIRST) and the FIRST methodology, harking back to the “FIRST in Motion – Wide Web Project” session from a day prior. Jason added three simple rules to tame the “gremlins” that creep up and attack a press:
- Follow established protocol
- Measure and maintain color
- No tweaking
He said that when it comes to print faults and troubleshooting, direction and frequency are clues. Streaks through the print in the web direction can be isolated to anilox (impacted cells, scoring), doctor blade (nicked, impacted debris or ink particle), idler roll (stopped and dragging), substrate (dragging web, often on dryer or ovens) or ink starvation (ink chamber dry, ink foamy). Streaks run across the web direction most commonly can be isolated to chatter (blade wear, blade pressure, blade alignment), balance and alignment (print cylinder, anilox, impression roll), gear marks (gear wear, proper pitch, will coincide with gear pitch and frequency) or bounce (gaps in print surface contact).
The first gremlin the foursome tackled was dirty print. Joel explained some of its typical causes: screening selection, min dot being too small or an lpi that’s too high. An immediate fix, he said, is to doublecheck your screening, but testing before even reaching the printing stage and automating workflows can prevent dirty print from ever becoming an issue.
“I think dirty means different things to different people,” PJ admitted, discussing the topic from the plate point of view. Issues he covered included unwanted ink blobs/ink in non-image areas, hard edges instead of highlights, and muddy screens or gradient issues. Typical causes of dirty print, he said, include broken or malformed highlight dots, polymer redeposit during processing, plate dot cupping or a plate loading up with ink. He said it is crucial to work with your plate supplier to avoid the issue in the future.
Kevin then looked at dirty print in the pressroom, citing incorrect anilox choice, ink chamber flooding, stray air on plates, missing kiss impression and having excessive plate impression or relief, and ink drying too fast as some possible causes. A printer should reset kiss impression, check pH and viscosity and confirm the anilox in use is the correct roller. “Preparation is key,” Kevin implored, calling back to the preventative measures listed off by the rest of the panel as a means to avoid dirty print when on press.
The second gremlin was slurred print. Joel pointed to slur targets as a great tool to determine slur, provided they are positioned correctly.
PJ explained slurred dots as appearing like avocados, as opposed to an ideally positioned dot resembling a volcano. “It’s important you have balance between the hardness of the plate and the hardness of the tape,” he noted. A swollen plate can also contribute to print slur. If your density is acceptable, a printer could move to a softer tape, but a common theme of “doing your homework”—here in the form of performing optimization trials ahead of time to find that ideal plate/tape combo—was called for.
Moving along to the pressroom perspective, Kevin called to substrate tension or press slip, incorrect repeats and overimpression as typical causes, and said good equipment maintenance and confirming impressions rollers are clean (“they’re critical at this point,” he cautioned) are best practices to avoiding the issue.
A “tricky gremlin,” according to Bobby, is poor solids. How do you fix poor solids immediately? “Double check!” Joel exclaimed, referring to your various settings. He also called on automation to avoid the problem before it happens. Examining poor solids from a color point of view, Bobby pointed to some typical causes and said a visual correction is a good immediate fix. To avoid them altogether, a printer needs to resolve poor solids during the optimization process.
PJ drew attention to a trio of plate-related causes of poor solids: polymer redeposit during processing, a plate coated with a repellent or inadequate tape selection (“softer tapes just don’t push enough against the substrate to give a good solid,” he explained). Immediate fixes include cleaning the plate with solvent (if ink beads are present), using a harder tape (if pinholing appears) or completely remaking the plate (if irregular spots appear). Again, he urged attendees to perform an optimization trial to avoid any tape-related issues and do that homework by putting together a cleaning procedure before running the press.
In the pressroom, low ink viscosity, out-of-balance ink chemistry, ink foaming, or the wrong anilox volume or plate-to-substrate impression can all be causes of poor solids. Once again, a kiss impressions and checking to make sure the correct anilox and ink are in use can fix the problem immediately. “Press time is precious,” Kevin noted, calling again for adequate preparation. Working with your substrate vendor is also essential.
“It all goes back to good process control and optimizing those variables in your system,” Catherine said, as she and Jason returned to the stage to pose audience questions to the panel. Advice offered in their responses included:
- “We’re finding new things out that we haven’t had to address before,” PJ said, regarding new plate technologies and how a printer can adapt to troubleshooting with specific plates. “Work with your vendors,” Kevin added. “Don’t be afraid to reach out to your suppliers,” Jason noted
- “If you optimize and know what your sweet spots are, that’s when the information can flow back to prepress and to the separator,” Kevin said
- “Lpi is either customer driven, and then you determine which anilox can be used, or it’s the reverse—the printer says what it knows it needs to use,” explained Bobby
- “Our goal is to make sure whatever you use to clean the plate doesn’t harm the plate,” PJ said, offering a suggestion of 100 percent ethyl alcohol, with up to 20 percent ethyl acetate. “Alcohol is no problem for the plate”
Gremlin No. 4 represented matching color. Joel used the analogy of mistakenly wearing one blue sock with one black sock, or going to buy a second can of paint and selecting a slightly different shade.
From a proofing standpoint, Bobby stressed the importance of understanding how the color is being made—is it with spot colors? Process color? Expanded gamut? Solids, dots or both? In color diagnosis, he cautioned to use the proper environment to obtain good measurements. And to ensure there wasn’t a swap made on the pressroom floor, check the ink, anilox and substrate in use are all correct.
If the color does not match the proof or visual standard supplied in prepress, it can typically be caused by bad curves or color separation, and can be avoided in the future with automation, Joel explained. He reiterated leaning on automation as a means to avoiding the issue.
Kevin called out “all 2,000 variables in the pressroom” as being potential causes of poor color matching. Following optimization standards and controlling the process, he said, are best practices to avoid the issue.
High Dot Gain
Bobby returned to offer visual examples of high dot gain, then passed to Joel to speak from a prepress standpoint. Choosing the wrong screening or incorrect curves are common causes, immediate fixes are to check your work and, once again, automation is key for long-term impact. “The more you can automate that process, the better chance you have of not making a mistake,” Joel said.
On the proofing and color side, printers can solve the issue of high dot gain by first determining if solids are correct. “Know your aim points,” Bobby said—is it to SCTV or Murray-Davies targets? And locate where exactly the minimum dot should be.
To fix high dot gain immediately, move to a softer tape (if solids allow the change), PJ said; if a printer thinks wear or swell are to blame, it should consider remaking the plates and also check with plate making equipment suppliers. High dot gain in plates can be avoided altogether with optimization trials to determine proper plate and tape combination, predetermining ink compatibility and working with plate suppliers to identify ideal plate and plate making conditions.
Once again, Kevin urged attendees to reset kiss impression as a pressroom solution to high dot gain. Printers should also perform a series of checks: ink density, for dot gain, to confirm anilox and to inspect impression roller.
The final issues the panel spoke about was a combination of three—chatter, banding and bouncing. Bobby spoke about the trio—light/dark variation across the web direction—with Joel explaining this can be fixed in the prepress stage by planning for the machine on which you’ll be printing. “Design for what your press can handle,” he suggested
Yet again, PJ pointed out, it’s a bad combination of plate and tape that can manifest in chatter/banding/bouncing; that typically occurs when the tape is too hard and/or the plate is too soft. Optimization trials can determine the best plate and tape combination. Printers can also look at special compressible sleeves and adapters which can dampen vibrations.
“It is the bane of any printer’s existence,” Kevin said to describe the problem. He urged listeners to calibrate and level print units, and discover equipment issues as they begin to appear, not when they become so severe they cause a total shutdown. “Look to your partners in tapes, sleeves and mandrels,” he added.
Returning to the stage, Jason pointed out that “We can’t forget about the random gremlins.” When the defect seems random and doesn’t coincide with the print repeat, he suggested to measure the distance between defects to see if it does coincide with the circumference of a press roller; from there, a printer can determine if the issue stems from an impression cylinder, anilox roller, idler roll or chill roll.
Preceding a second Q&A opportunity, Catherine reiterated the session’s refrain: Process control is critical, and referred to FIRST 6.0 as “our industry’s survival guide.” In that second question and answer opportunity, the panel offered additional words of wisdom that included:
- “The nature of the problem is kind of the clue—Did it change suddenly or subtly?” Kevin asked
- On the topic of plate life, PJ said harder plates should wear better, but variables like impression (a small difference can have a long-term impact), ink type and substrate (something coarser, compared to a film) play a big part. “There are a lot of principles that can give you the nuts and bolts to achieve” a long-lasting plate, he added.
- “Plate storage is a big part of that, as is how you clean your plate and how you take it off the cylinder,” Joel added.