Process Control Is Key to Effective Ink Optimization

Whether it occurs on a particular press during a single run or among different presses, color variation is a natural part of the print reproduction process. It is also anathema to packaging end-users, for whom color consistency on the shelf is a critical element of a product's appeal to the customer. At the same time, increasing cost and deadline pressures have raised the stakes for converters to print jobs quickly and efficiently, match the proof, use as little ink as possible, and generate minimal waste. One of the keys to efficient package printing, therefore, is understanding the source of unwanted color variation and implementing measures to drive those deviations out of the process, eliminating the need to take costly corrective action at the press.

While ink usage represents only a small fraction of the overall cost of a print job, it can have a significant impact on pressroom efficiency and the quality of the finished product. As a result, effective ink management techniques—specifically, ink optimization solutions—have assumed competitive importance as a means of stabilizing the printing process and achieving cost savings.

Various ink optimization solutions on the market aim to ameliorate color variation, reduce ink usage, cut costs, and boost productivity by:

• Improving printing conditions;

• Promoting faster makereadies, shorter drying times, and faster finishing;

• Reducing waste; and

• Producing from 15-25 percent savings on ink, depending on the process and substrate involved.

Benefits are also said to include improved reproduction quality; better neutrals; more consistent total ink coverage; and easier color space transformations, as well as cleaner (greener) runs, faster absorption, reduction in rub-off, and potentially higher printing speeds.

Shades of gray

In all cases, the mechanism for achieving ink optimization is known as GCR or Gray Component Replacement, which changes the separation of an image by taking color from the file and increasing the black channel, resulting in a visually and spectrophotometrically nearly identical separation that uses less ink. This, in turn, improves the quality and consistency of the printed result in cases where unwanted tinting of the plate occurs. This is especially useful for high-speed web presses, where a color shift on press could affect many sheets in a short period of time. Long-run sheetfed work also will benefit, yielding consistent, repeatable color during the entire press run. Cost savings result, in part, because cheaper black ink is used replace the more expensive CMY variety.

In point of fact, says Marc Welch, vice president of sales for GMG (www.gmgcolor.com), "Smart printers have been doing this for years. What's driving the current focus on ink optimization in the packaging market is that people are beginning to look closely at ways to decrease color variation and increase the color consistency of products on the shelf."

However, he observed, the full value of an ink optimization solution is best realized where appropriate process controls have been implemented to ensure that press, proof, incoming files, and CtP curves are properly aligned to a given specification (target, densities, dot gain value, etc.).

Maintaining consistent image color during a press run typically starts in prepress and involves evaluating the color separation process, taking into account the ink, ink properties, substrate characteristics, and press condition. "Over the past five years or so, we've become more aware of the problem and have started to detect and measure color inconsistencies and to nail down a number of troublesome variables," Welch said.

Eliminating film-based workflows in favor of computer-to-plate has helped, but problems persist. The difficulty is especially acute in folding carton production, where the color inconsistency is rooted in super-high-density ink coverage.

By the numbers

According to Welch, problems stem from a fundamental disconnect between the prepress activity involved in creating the file and the needs of the package end-user. Especially troubling, he said, are "generic CMYK separations" that fail to take into account the type of press, ink, ink properties, substrate, and overprint characteristics associated with the job.

To a large extent and despite the adoption of digital workflows, he says, "We're still stuck in film concepts." That is, "When prepress companies made the color separations and proofed from film, and shipped both film and proofs to the printer, the press would be made to match the analog proof. We now substitute a 1-bit data file for each color and ship a 'locked-down' digital file to the printer without tuning the file to the press. We need to get away from 1-bit workflows," Welch explains.

In digital workflows, calibration in prepress is defined by how the press prints. Regardless of the specification in question (flexo's FIRST is a good example), printing "to the numbers" will result in more consistent color—but only if operators follow the specification closely from job to job, shift to shift, and day to day, using the appropriate measurement devices and other tools.

There's more to ink optimization than reducing the amount of ink that is used, Welch insists. "Color management on the back end is a prerequisite to deriving the full benefit of ink optimization. You need to characterize the press, set up a standard, and understand what the press wants to do."

"Consumer product companies would love to have more and better process controls," Welch says, "but, in order to achieve it, more education, adjustment, and measurement need to take place—and everybody needs to sign up." pP