Quality Control: Measure it, Control it!

The roles of quality control (QC) equipment and systems in the pressroom and in the prepress area are related, but distinct. By the same token, color management and color process control are related, but are separate concepts. While color management means managing your devices such that you output color accurately and consistently, quality control or color process control ensures that the color will be consistent across processes and substrates. QC clearly represents a very specific challenge in packaging, given the variety of different substrates and disciplines commonly applied to a given brand.

Nevertheless, color process control has had a tough row to hoe for packaging printers, who initially failed to understand the need for robust, reliable instrumentation designed to verify and calibrate the output of their computer-to-plate systems. This month, packagePRINTING speaks with several instrument suppliers to clarify some of the issues surrounding the role of color process control in enhancing reproduction quality, color control, and productivity.

Risky business

According to Larry Goldberg, director of engineering for Beta Industries, for the many thousands of pieces of output created every hour in the pressroom, a variety of simple or sophisticated QC measures can be applied. These include statistical sampling or visual inspection and density spot checks or full sheet scans, depending on the customer’s expectations and the capabilities of the pressroom, where it is generally accepted that some waste and spoilage will occur. In contrast, materials created in the prepress department carry a much higher risk. “For example,” Goldberg says, “a bad plate can idle a press chargeable at hundreds of dollars per hour. Even when a plate appears usable, precious time is often wasted tweaking it on press, even adjusting inks or anilox rolls.”

To alleviate these risks, different instruments, including densitometers, colorimeters, spectrophotometers, and plate analyzers, were developed to detect and measure color changes at various stages in the workflow. Densitometers determine the strength of a color from its density, usually derived from ink film thickness. Colorimeters, such as X-Rite’s 528 handheld unit, break down color into its numeric value using the CIE XYZ color space or one of its derivatives, such as CIE L*a*b or CIE L*u*v. Spectrophotometers measure spectral data, which form a complex set of data on the spectral curve. Spectrophotometers gather the most complete color data and provide the most accurate and useful color information.

According to Chris LaFontaine, X-Rite’s global product manager for printing, “Instrumentation converts color appearance to numerical values. This helps to compare and define colors more accurately than is possible by appearance alone. The degree of color accuracy that is achieved depends on the types of instruments used at various points in the workflow.”

Of densitometers, “Knowing your ink densities helps you ensure proper ink coverage, but doesn’t guarantee accuracy in shades of color,” LaFontaine explains. “Colorimeters and spectrophotometers more accurately define colors and, therefore, are better at ensuring that colors truly match. However, because proofing and print processes are different, the final piece still may look ‘off,’ even when the color patches between the proof and the printed substrate match.” This “subjective color shift” occurs when tone value increase causes the color to look “off,” even when it isn’t, he says. Plate analysis is helpful in making sure that the press matches the continuous-tone image that produces the color as it was meant to be visualized.

When systematic, consistent quality controls throughout the workflow are absent, ad hoc tweaking can result in costly delays, unnecessary waste, and expensive rework, LaFontaine continues. While commercial printers tend to be more attentive to color control than package printers, due to their handling of color-critical marketing materials, that situation is changing rapidly as packaging becomes more important to the saleability of the product, he adds.

From X-Rite

X-Rite (recently combined with GretagMacbeth) manufactures products geared toward both color management and color process control. Its portfolio of solutions includes the ProfileMaker Packaging Module with MultiColor Plugin PhotoShop and GoP-Generic Output Profile for non-traditional process printing; IntelliTrax Auto-Scanning System for evaluation of ink density, deltaE, hue error and grayness, gray balance, dot gain, trap; and the new Platescope device for plate process control.

LaFontaine points out that PlateScope supports all current screening technologies, including AM, FM, XM, and transitional screen types. In addition, X-Rite also offers the vipFlex desktop flexo plate reader; the vipPAQ in-line 9-band densitometer for real-time monitoring of roll-to-roll flexography; as well as the Eye-One color management solution and Eye-One iO Automated Scanning Table.

Control issues

“Troubleshooting press problems is much easier with data from each piece of the puzzle. After all, you can’t control what you can’t measure. Measuring dot sizes on the plates provides the means to consistent reproduction. Problems can be found before going to press, eliminating costly downtime and rework,” says David Allen of The Provident Group.

For the flexo printer, Allen says, the anilox roll and the printing plate are probably the two most important variables to control when going to press. Too often, however, when a job is not working, the printer will blame the ink supplier, the ink supplier will blame the anilox roll manufacturer, and the anilox supplier will blame the plates. Accurate measurement of cell volume enables predictable ink film thickness. Combine that certainty with predictable dot sizes on plates, and printers have the power to reduce makeready and color match time and deliver consistent results every time a job goes to press.

To address these issues, The Provident Group markets the FlexoCAM and AniCAM solutions developed by Troika Systems in the United Kingdom. Less than one year old and new to the U.S. market, FlexoCAM is a portable, PC-based camera/microscope that measures dot sizes on film or masks, printing plates (including in-the-round sleeves or cylinders), and printed copy. It is said to be the first product that allows companies using in-the-round technologies to see and measure dots easily on mounted plates before, during, and after a production run‑letting printers know what size highlight dots are being held on the plate. The AniCAM system measures cell volume on anilox rolls. It is in the final testing stages, with commercial release scheduled for the end of the third quarter 2006.

Ouch! Not the rubber ruler!

Goldberg believes it has taken years for printers to understand the need for quality control tools. In fact, he maintains, the idea that flexo plates can be measured at all has not yet sunk in, although he acknowledges that the offset industry has been aware of the need for plate measuring systems “a little longer.” With flexography in particular, he says, the difficulty stemmed from the perception that flexo platemaking “(had) no dot gain, no variability in the front and back exposing devices, completely uniform and non-varying washout process, and was immune to human error.” To the extent this attitude persists, Goldberg says, the results of inattention to plate process control can be dire in terms of both quality and productivity.

“‘Put it on the press and we’ll find out’ is worse than the rubber ruler concept,” he says. “You are taking the output of a process with a dozen variables (the plate) and using a process with six dozen variables (the printing press) to ‘measure’ it. The trouble with this situation is easily demonstrated when re-running a job. It should be trivially simple to obtain the same result on press, but it is not.”

Beta Industries supplies the Betaflex 334PQF photopolymer plate analyzer; the Beta UltraDottie II offset plate analyzer; the Betacolor S4 Xpress Pressroom Densitometer with Gray Balance Target Detection; and the Betacolor 2000 Seven-Color Spectro-Densitometer for the unique challenges presented by extended color printing. pP