On a night when a monstrous record-breaking windstorm swept the country, hurricane force winds tore trees out by their roots, ripped roofs from homes and put semi trucks onto their sides. While nature seemed out of control, the presentations at the October meeting of the FTA Great Lakes Group (GLG) focused on the importance of keeping the flexo process in control.
Fitting, then that the meeting was held at Quad Tech in Sussex, WI. Quad Tech engineers and manufactures 100 percent print inspection and defect detection systems capable of speeds up to 3500 fpm, color control and verification systems utilizing true spectrophotometer response and color-to-color registration systems that control registration laterally and in the web direction.
Attendees had the opportunity to tour Quad Tech’s facility and see demonstrations of a wide array of inspection and control solutions in action. The Quad Tech designed inspection system canvases the entire web, makes an overall template they refer to as a “golden master”, and performs delta E color monitoring for deviation through the print run using color line scan technology. This process creates a map of the roll with position data for detected defects. This information is passed on to the waste management system connected to the slitter/rewinder, which automatically rewinds to the position where defects are located. At the conclusion of the tour, the technical presentations began.
Color Control
A major objective in printing is control of color. In order to control color, you have to be able to measure it. But what is important to measure and why? Which tool(s) provide the full range of information needed to produce repeatable color? According to John Seymore, (introduced as “the Mad Scientist”), paint manufacturers have a way of identifying color. They might call it “strawberry rhubarb”. Consumers may pick out a color swatch and decide they want their front room painted in such a color. Unfortunately, there is not a “strawberry rhubarbometer” that can be used to quantify and verify that color.
For flexo printers, there needs to be a way to identify and communicate color more scientifically. As a result, several methods and measurement instruments have been developed that allow us to measure such things as RGB values, spectral data, density and CIELAB values. But which is best and why? John contends that what we should measure is CIELAB values.
CIELAB refers to a set of three numbers we can use to uniquely identify color numerically. L*A*B* values represent a position in color space. CIELAB is important because it provides a standard for representing color that the printer and print buyer can agree upon.
While RGB values can help measure deviation from a standard and assure that Delta E values are staying in tolerance, there are issues with RGB measurement technology. RGB values are measured with an RGB camera. RGB cameras produced by different manufacturers and even different cameras from the same manufacturer can have a different spectral response. In other words, they all see color differently. More importantly, they respond to color differently than the human eye. A different spectral response to the same color is known as metamorism.
When it comes to measuring density, the effect of metamorism is even worse. Densitometers measure density, but have a very different response to color than the human eye. In addition, densitometers are less sensitive or “color blind” to certain ranges of the light spectrum. As a result, ink density may be correct when the color is not.
Densitometers were designed to look at (receive a spectral response from) three channels: cyan magenta and yellow. That would not be a problem if all printers printed with was those three colors, but much of flexo printing is done with specialty colors. To print accurately with the entire range of colors represented on the pages of a Pantone book, you would need a different densitometer engineered with a channel calibrated for each color you are printing.
A colorimeter has sensors that respond similarly to color as the human eye and is capable of obtaining CIELAB values.
Spectral data is obtained from spectrophotometers. A spectrophotometer has many more channels that each provide response to a narrow range of color. By applying a mathematical formula to the data produced by these channels, you can simulate the response of any of the color quantifiers including CIELAB values. This makes spectrophotometers by far the most versatile of the color measurement instruments.
In short, for those wanting a means to control color and have a predictable, measurable, quantifiable and meaningful way to represent it, you need an instrument that “sees” color the way a human eye does.
Automatic Preprogrammed Press Control
To have precise control over the placement of color, it is critical to have proper registration and impression. While in the past, these adjustments were eyeballed on inexpensive, unsophisticated presses, precise ink placement control requires these processes be automated. As a result, equipment engineers developed sophisticated software and hardware solutions to monitor and self-adjust on-the-fly to maintain precise control over the mechanical variables that affect color placement.
In his presentation, Denny McGee, President of MPS America, (Denny McGhoul for purposes of this event), talked about how automation and servo technology in particular, reduces waste, improves print quality, increases output, drastically reduces make-ready time, and reduces unnecessary wear and tear on press components. Modern label presses utilize the application of servo technology to provide stable web transport and consistent registration through the entire operating range of press speeds.
While older presses often had multiple mechanical adjustment points, the addition of servo control to the print heads at each press station insures precise control of the impression between anilox and plate. Information programmed in to the control system about various parameters for the job including printing plates, sticky-back thickness, and web thickness provides a baseline stored digitally so they can be recalled to eliminate manual operator adjustment on repeat jobs.
With automatic print control, the machine essentially sets itself up. Print sleeves reinstalled in the machine are automatically rotated into an ideal registration position. Then the machine adjusts for proper impression. As it starts to print, a camera system verifies and fine-tunes registration in the web direction either mark-to-mark or mark to cylinder. A separate servo adjusts lateral registration, while another one yet adjusts for the specific web thickness of the job. Because the impression cylinder free-idles, it matches the speed of the plate to that of the web 100%, eliminating some of the problems label printers have experienced with banding and marking, particularly with pastel tints at high plate screens.
The entire machine is control from the keypad or an “I-control” knob (a multiple adjustment dial), which lights up to indicate if the machine is in set-up or run mode. The control system monitors press functions providing real-time feedback to the operator and notifying them of any problems as they arise so they can be promptly addressed and corrected. This reduces waste and increases productivity against a wide range of market applications.
Reproduction Control
While control of the mechanical functions of the press is extremely important, where the rubber hits the road is at the tops of the plate dots. Here it is critical to control dot geometry and dot size in order to control dot gain. According to Dave Recchia, Sr. Printing Process Specialist for MacDermid Printing Solutions, the conversion from analog to digital technologies has produced tremendous results, but better yet is a plate architecture that combines the best attributes of both.
With this new process the plate dots have flat tops similar to analog, but a more column-like profile characteristic of digital plates. The flat tops provide consistent impression surface requiring less impression. The result is longer plate life and reproducible highlights at higher line screens along with an extended grayscale range. The tubular wall profile is less susceptible to impression-induced gain, and does not cause increased gain as the plates wear.
A side benefit from the flat plate tops and reduced impression is a tremendous improvement in reducing horizontal banding in fluted stock over analog or conventional digital plates. By better controlling the dot size from the peaks to valleys of the flutes, the consistency of the print is significantly enhanced.
A conventional digital plate requires a bump curve (7% in the mask translates to 1% tonal range in the plate). The bump compresses the remaining grayscale, limiting the overall tonal range available to print. A hybrid plate process results in a 1:1 mask to plate reproduction, which removes variability from the imaging process and eliminates the bump curve step from the process workflow.
FTA Great Lakes Group
As each speaker spoke something resonated throughout the building, but it was not the wind. An overriding theme emerged like a ghost ship coming out of the fog: control; controlling the dot structure on plates, controlling mechanical attributes of the press including registration and impression, and controlling color. Needless to say, the Great Lakes Group was blown away by the technical content of the meeting.
With Halloween just a few days away, the meeting room had a festive, if not spooky atmosphere provided courtesy of a variety of ghoulish figures and ghostly images. With food and refreshments sponsored by Package Printing Converting Technologies and Solutions (PPCTS) and a decorated cake from D.J. Lanska & Associates, the meeting was a combination of technical conference, networking event and holiday party.
FTA Great Lakes Group meetings are open to all printers, suppliers and consumer product companies. There is no fee to join the group, but there is a charge to attend the meetings. Typically, FTA members pay $10, non-members pay $20. Students and faculty in graphic arts programs are free. Meeting proceeds go to support the FFTA scholarship fund.
Meetings take place at host sites, which can be printers, suppliers or educational institutions roughly from Chicago to Green Bay, WI. Tours provided by the host sights enhance the educational value of the meetings. Sponsors provide food and refreshments for the meetings. Anyone interested in participating as a host site, speaker or meeting sponsor is encouraged to email david.lanska@yahoo.com.
Information about upcoming events is posted on LinkedIn, Facebook and Twitter. The GLG also has a fan page on Facebook and a group on LinkedIn. (a subgroup of the FTA Linkedin group).
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