CLOSED-LOOP COLOR CONTROL — SMALL CHALLENGES, BIG REWARDS
THE WORLD of closed-loop color control (CLC) somewhat resembles a PGA-caliber golf course. In both cases, the rewards for mastering it are high, but hazards along the way can certainly leave you in a tough spot.
What some web offset printers agree upon is this: closed-loop color control is a tool, not a turnkey panacea that will solve all color reproduction issues. Perfect, it is not.
Generally speaking, CLC is a process where the control system analyzes printed color bars at full web press speeds and makes on-the-fly adjustments to maintain accurate color control.
“The biggest challenge is getting our internal and external sales teams on board with the fact that closed-loop color control systems are a tool, not a cure-all,” notes Russ Welch, pressroom manager for Ripon Printers of Ripon, WI. “Just because you have these systems does not mean you have perfect color on every job with any type of color or format. It helps you to get to pleasing color much faster, which gets product on the skid faster.”
According to Welch, Ripon Printers runs 99 percent of the time controlling color to gray balance with QuadTech Classic, running to density only when necessary. With an average makeready of about 1,600 impressions and a varied run mix ranging from an eight-page signature on SCA stock to a 32-page form on 70-lb. paper, Classic has helped to enable that versatility for Ripon.
What has allowed Ripon to be competitive in this regard is the reduced makeready waste savings. Staffing issues are also improved; with a two-web stack and a small footprint, Ripon has been able to reduce manning from four operators to three. Eliminating subjective color judgment frees press operators to do other things.
Running to dot gain can be challenging, according to Welch. He notes that the CLC system needed some tweaks in the manner in which it was reading dot gain versus solid density. While running in dot gain control, variables in the press run can provide challenges—substrate issues, blanket piling or water levels, to name a few.
“The beauty of these new tools is the ability to see these variables change and correct them in real time,” Welch says. “Without this type of system, print defects go unnoticed for longer periods of time.
“We do a pretty good job of matching our digital proofs, given the technology of proofing available today,” he adds. “To do this by hand on-press would cost much more in press time and waste. If we change inks or some other products, we are just a press run away from updating the prepress profiles for proofing.”
Speaking of Wisconsin printers, Menasha-based Banta has a total of nine closed-loop color control systems installed on web presses across its publication platform. Andy Johnson, vice president and general manager of Banta Publications-Kansas City, notes that the systems have a learning algorithm for ink presets. That algorithm changes when a job is saved, and the CLC system recognizes the difference between the saved settings and the presets on the fountains. The next time a job is run, the settings are more accurate.
Reduced makeready time and run waste were the primary justification variables for obtaining them, according to Johnson. Consistency of color, from the beginning of the run until the end, is the hallmark of closed-loop color control for many printers, Banta included.
“One of the ‘bells and whistles’ on the system that provided improvements is the measuring of dot gain,” Johnson notes. “That’s helped free our pressmen up, so they’re focusing less on color control. It’s a benefit we never had; before we had to manually measure our dot gains and determine if they were too high based on color reproduction and matching the proofs.”
The upshot: press operators can now take a proactive instead of a reactive approach and make improvements during the press run, says Greg Hain, pressroom manager for Banta. “Before, if we didn’t match a proof, an operator might say, ‘that’s as close as I can get it,’ because he may not have taken the time—especially on short runs of about 20,000—to perform a lot of hand-held readings,” Hain remarks.
“Now you just press a button and there are all your dot gains, across the page, for every color. You know whether a problem is print related or an issue with a supplied proof.”
Banta also reaped an interesting revelation that indicated getting color up to ‘lap speed’ was not always the final issue that held a job up from producing sellable copies. After the CLC system was installed, a “last thing that kept you from saving” chart was put on the press. Sometimes problems centered around folds, register motors moving slower than desired, or web guides slowing and binding up. In essence, the CLC helped draw attention to deficiencies elsewhere during press runs.
A Web Printing Controls (WPC) closed-loop color control system is just one cog in a CIM workflow at Lane Press in Burlington, VT, which includes an MRP system, platemaking technology and integrated color-to-color register.
The printer can now, among other things, preset more press functions to net register, tension, web positioning and fold adjustments, as well as control color, notes Charlie Foell, press manager.
Foell, like others, notes that press chemistry must be held to tighter tolerances to optimize CLC. During one run, a new batch of solution was not producing favorable results; a subsequent lab workup revealed that a slight change in the solution created instability.
“Initially we thought we had calcium buildup in the ink train from calcium-based papers that created stripping,” Foell says. “It’s an old problem these days—calcium builds up in the ink rollers, which attracts water first, then the ink rides poorly on top of the water.
“What was really happening was that the water wasn’t going into the ink as well as it should have. (The water) had no place to go, so it would kind of surf on top of it. The closed-loop color system would ‘chase’ itself; it read the excess water and emulsification as low density, which forced the inking levels up, forcing the water elsewhere. While the fountain solution was the primary culprit, we know the ink changed a bit, too. We put a lot of effort into nailing down chemistry issues instead of throwing more chemicals at them.”
The onset of closed-loop color control has allowed Trend Offset Printing, Los Alamitos, CA, to do away with contract proofs. Also a QuadTech customer, Trend Offset runs to solid ink density while monitoring dot gain and print contrast, notes John Bryant, chief information officer. One of the primary benefits, according to Bryant, is the consistency that CLC provides.
“We have numerous clients with multiple locations. One in particular has 23 publications that we print throughout the month, with like ads appearing in them,” he reveals. “CLC brings repeatability and predictability for the client. Whenever an advertiser sees their ad from version to version or issue to issue, they see the same ad reproduction. That’s probably the single biggest reason we brought CLC to Trend Offset Printing.”
Even so, closed-loop systems can present a challenge when it comes to calibrating equipment and reporting. For instance, Bryant notes that a hand-held spectrophotometer will provide consistent color measurement from press to press, yet the CLC system will have slight deviations from press to press. Thus, if a buyer is having work printed across several presses, he/she may be led to believe that everything is not being printed exactly the same. And if a client requests reports on a regular basis, the printer may need to interpret variations in data that are expected to be consistent.
The benefits far outweigh the glitches that arise on occasion, though, and Bryant is quick to point out that QuadTech is highly responsive to even the smallest of problems. To him, the proof is in the repeatability and predictability.
“Everyone interprets color differently,” he says. “With the CLC system, human interpretation comes out of the equation; the optics and the algorithms take over.”
That means more birdies, less bogies—an acceptable par for the printing course.
